JP2010027297A - Fuel battery system, operation method of fuel battery, and fuel battery vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel battery system which recovers the power generation performance of a fuel battery and improves the durability of the fuel battery. <P>SOLUTION: The fuel battery system includes the fuel battery 10, status detecting means 50 and 60, a potential determining means 90, and potential control means 30, 70, and 90. The fuel battery 10 contains platinum as an electrocatalyst. The status detecting means 50 and 60 detect the state of the fuel battery 10. The potential determining means 90 determines target potential equivalent to a target value of the air electrode potential of the fuel battery 10 based on the detected state of the fuel battery 10. The potential control means 30, 70, and 90 recover the power generation performance of the fuel battery 10 by lowering the air electrode potential of the fuel battery 10 to the determined target potential. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell system, a fuel cell driving method, and a fuel cell vehicle.

  In recent years, fuel cells have attracted attention as a power source with a low environmental load. A fuel cell receives power from oxygen and hydrogen and generates electric power. In a fuel cell, platinum or a platinum alloy is used as an electrode catalyst.

As a technique related to a fuel cell containing platinum as an electrode catalyst, a fuel cell device as shown in Patent Document 1 below is known from the viewpoint of suppressing a decrease in power generation performance due to oxidation of the platinum catalyst. In the fuel cell device disclosed in Patent Document 1, the cathode potential (air electrode potential) of the fuel cell is periodically set to 0.6 Vvs. The platinum oxide is reduced by lowering it below SHE, and the performance of the fuel cell is recovered.
Special table 2003-536232 gazette

  However, the fuel cell device has a problem that platinum is dissolved by repeated oxidation and reduction of platinum, and the performance of the fuel cell is deteriorated in the long term.

  The present invention has been made to solve the above problems. Accordingly, an object of the present invention is to provide a fuel cell system and a fuel cell operating method capable of restoring the power generation performance of the fuel cell and improving the durability of the fuel cell.

  Another object of the present invention is to provide a fuel cell vehicle equipped with the fuel cell system.

  The above object of the present invention is achieved by the following means.

  The fuel cell system of the present invention includes a fuel cell, a state detection unit, a potential determination unit, and a potential control unit. The fuel cell contains platinum as an electrode catalyst. The state detection means detects the state of the fuel cell. The potential determining means determines a target potential that is a target value of the air electrode potential of the fuel cell based on the detected state of the fuel cell. The potential control means restores the power generation performance of the fuel cell by lowering the air electrode potential of the fuel cell to the determined target potential.

  The fuel cell operation method of the present invention includes a state detection stage, a potential determination stage, and a potential control stage. In the state detection step, the state of the fuel cell containing platinum as an electrode catalyst is detected. The potential determination step determines a target potential that is a target value of the air electrode potential of the fuel cell based on the detected state of the fuel cell. The potential control step restores the power generation performance of the fuel cell by lowering the air electrode potential of the fuel cell to the determined target potential.

  The fuel cell vehicle of the present invention is equipped with the fuel cell system as a driving power source.

  According to the fuel cell system and the fuel cell operation method of the present invention, the target potential of the air electrode potential that is lowered to restore the power generation performance of the fuel cell is changed according to the state of the fuel cell. It is possible to reduce the platinum oxide while suppressing dissolution. Therefore, the power generation performance of the fuel cell can be restored and the durability of the fuel cell can be improved.

  According to the fuel cell vehicle of the present invention, since the durability of the fuel cell is improved, the reliability of the fuel cell vehicle is improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following embodiment, a case where the present invention is applied to a power supply system of a fuel cell vehicle will be described as an example.

(First embodiment)
FIG. 1 is a diagram showing a schematic configuration of a fuel cell system according to a first embodiment of the present invention. The fuel cell system according to the present embodiment reduces the cathode potential of the fuel cell to a potential of 0.6 V or 0.8 V with respect to the reversible hydrogen electrode potential (RHE) according to the state of the fuel cell. The power generation performance of the battery is restored.

  As shown in FIG. 1, the fuel cell system 100 of the present embodiment includes a fuel cell 10, a fuel tank 20, a compressor 30, a voltage detection unit 40, a temperature detection unit 50, a resistance detection unit 60, a loader 70, and a current detection unit. 80 and a control unit 90.

  The fuel cell 10 is supplied with hydrogen and oxygen to generate electric power. The fuel cell 10 is configured by stacking a plurality of single cells as unit cells. Each single cell uses platinum as an electrode catalyst. A detailed configuration of the fuel cell 10 will be described later.

  The fuel tank 20 stores anode gas (fuel gas containing hydrogen) supplied to the fuel cell 10. The fuel tank 20 supplies anode gas to the anode (fuel electrode) of the fuel cell 10 through a hydrogen supply pipe.

  The compressor 30 supplies a cathode gas (for example, air) to the fuel cell 10. The compressor 30 is connected to the cathode (air electrode) of the fuel cell 10 through an oxygen supply pipe. The compressor 30 of the present embodiment is controlled by the control unit 90 and supplies cathode gas to the cathode of the fuel cell 10.

  The voltage detection unit 40 detects the cell voltage of the fuel cell 10. The voltage detector 40 includes a voltage sensor attached to the fuel cell 10 and detects the cell voltage of one single cell among the plurality of single cells constituting the fuel cell 10. The voltage detection unit 40 is electrically connected to the control unit 90, and a signal from the voltage detection unit 40 is transmitted to the control unit 90.

  The temperature detection unit 50 detects the temperature of the fuel cell 10 as temperature detection means. The temperature detector 50 includes a temperature sensor and detects the temperature of the fuel cell 10. The temperature detection unit 50 is electrically connected to the control unit 90, and a signal from the temperature detection unit 50 is transmitted to the control unit 90.

  The resistance detector 60 detects the resistance value of the fuel cell 10. The resistance detector 60 includes an ohmmeter that is electrically connected to the fuel cell 10 in parallel, and measures the electrical resistance value of the fuel cell 10. In addition, the resistance detection unit 60 functions as a moisture content detection unit that detects the moisture content of the fuel cell 10. The resistance detection unit 60 is electrically connected to the control unit 90, and a signal from the resistance detection unit 60 is transmitted to the control unit 90.

  The loader 70 extracts current from the fuel cell 10. The loader 70 is electrically connected to the fuel cell 10 in parallel, and consumes or stores electric power generated by the fuel cell 10. The loader 70 of the present embodiment includes a drive motor for driving a fuel cell vehicle, an auxiliary device of the fuel cell 10, and a secondary battery. The loader 70 is controlled by the control unit 90 and extracts current from the fuel cell 10.

  The current detection unit 80 detects a current flowing through the fuel cell 10. The current detection unit 80 includes an ammeter provided between the fuel cell 10 and the loader 70, and detects a current flowing between the fuel cell 10 and the loader 70. The current detection unit 80 is electrically connected to the control unit 90, and a signal from the current detection unit 80 is transmitted to the control unit 90.

  The control unit 90 controls the compressor 30 and the loader 70. The controller 90 controls the compressor 30 and the loader 70 to lower the cathode potential of the fuel cell 10. Control unit 90 receives signals from voltage detection unit 40, temperature detection unit 50, resistance detection unit 60, and current detection unit 80, and transmits a command signal to compressor 30 and loader 70. The compressor 30, the loader 70, and the control unit 90 function as potential control means. Further, the control unit 90 determines the target potential that is the target value of the cathode potential of the fuel cell 10 based on the temperature and water content of the fuel cell 10 detected by the temperature detection unit 50 and the resistance detection unit 60. Part (potential determination means).

  Next, the fuel cell 10 of the present embodiment will be described in detail with reference to FIG.

  FIG. 2 is a perspective view showing a cell structure of the fuel cell in the fuel cell system shown in FIG. As described above, the fuel cell 10 of the present embodiment is configured by stacking a plurality of single cells as unit cells that generate an electromotive force by the reaction between the anode gas and the cathode gas.

  As shown in FIG. 2, each single cell 11 constituting the fuel cell 10 includes an MEA 12 and separators 13 disposed on both surfaces of the MEA 12.

  The MEA 12 includes a solid polymer electrolyte membrane 14 and an anode 15 and a cathode 16 that sandwich the solid polymer electrolyte membrane 14 from both sides. The solid polymer electrolyte membrane 14 is composed of a polymer electrolyte membrane that passes hydrogen ions. The anode 15 includes an anode catalyst layer 15A and a gas diffusion layer 15B, and the cathode 16 includes a cathode catalyst layer 16A and a gas diffusion layer 16B. The cathode catalyst layer 16A contains platinum (Pt) as an electrode catalyst. The cathode catalyst layer 16A is made of platinum particles supported on a carbon powder carrier, for example. Note that unlike this embodiment, a platinum alloy such as a Pt—Mo alloy, a Pt—Fe alloy, a Pt—Ni alloy, and a Pt—Co alloy may be used as the electrode catalyst.

  The separator 13 is formed of a conductive material. In an active region that contributes to power generation on one side of the separator 13, a groove portion 17 that forms an anode gas flow path 17 </ b> A through which the anode gas flows through the MEA 12 is formed. On the other hand, in the active region on the other surface of the separator 13, a groove portion 18 is formed that forms a cathode gas flow path 18 </ b> A through which the cathode gas flows through the MEA 12. The anode gas is introduced from the anode gas inlet, flows through the groove portion 17, and is discharged from the anode gas outlet. The cathode gas is introduced from the cathode gas inlet, flows through the groove portion 18, and is discharged from the cathode gas outlet.

  When the anode gas and the cathode gas are circulated through the anode gas channel 17A and the cathode gas channel 18A, respectively, hydrogen is converted into hydrogen ions by the catalytic action of the anode catalyst layer 15A, and electrons are released. The hydrogen ions that have released the electrons pass through the solid polymer electrolyte membrane 14. In the cathode catalyst layer 16A, hydrogen ions that have passed through the solid polymer electrolyte membrane 14 and electrons that have passed through an external circuit (not shown) react with oxygen contained in the cathode gas to generate water. By this action, the anode 15 becomes negative and the cathode 16 becomes positive, and a DC voltage is generated between the anode 15 and the cathode 16 as shown in FIG. In the present embodiment, this DC voltage is detected by the voltage detector 40. It should be noted that this DC voltage is ideally 1.23 V in a state where no current is applied. However, since the fuel cell has an internal resistance, the voltage detected by the voltage detector 40 is lower than the ideal voltage.

  According to the fuel cell system 100 of the present embodiment configured as described above, the target potential is determined based on the state of the fuel cell 10, and the cathode potential of the fuel cell 10 is lowered to the determined target potential. The power generation performance of the fuel cell 10 is restored. Hereinafter, a method for operating the fuel cell in the fuel cell system 100 of the present embodiment will be described with reference to FIGS.

  FIG. 3 is a flowchart for explaining a fuel cell operating method by the fuel cell system of the present embodiment.

  As shown in FIG. 3, in the fuel cell operating method of the present embodiment, first, it is detected that the operation of the fuel cell 10 is continued in the oxidation region where the platinum catalyst is oxidized (step S101). Specifically, for example, by determining whether or not the state in which the cell voltage (or cathode potential) of the fuel cell 10 maintains a value of 0.8 V or more continues for a predetermined time or more, The continuation of the operation of the fuel cell 10 is detected. Note that the state in which the operation of the fuel cell in the oxidation region is continued is a state in which the fuel cell vehicle has been idling for a long time, for example, in a traffic jam. In such a low load operation state, the oxidation of platinum proceeds and the cell voltage slowly decreases.

  Next, the target potential of the cathode potential that is lowered to restore the power generation performance of the fuel cell 10 is determined (step S102). In the present embodiment, based on the temperature and water content of the fuel cell 10, 0.6 Vvs. RHE or 0.8Vvs. A target potential for RHE is determined. Details of the process for determining the target potential will be described later.

  Next, the cell voltage per unit cell 11 of the fuel cell 10 is detected (step S103). In the present embodiment, the voltage detection unit 40 detects the voltage of one single cell 11 constituting the fuel cell 10 as the cell voltage.

  Next, the coverage of platinum used as a catalyst is calculated (step S104). In the present embodiment, for each material used in the fuel cell 10, a cell voltage-coverage conversion table showing the relationship between the cell voltage and the coverage is determined in advance, and the cell calculated in the process shown in step S103. The coverage is calculated according to the voltage. Note that the lower the cell voltage, the higher the coverage.

  Next, it is determined whether or not the material covering platinum is only platinum oxide (step S105). In the present embodiment, the platinum coverage determined in advance for each material corresponding to the predetermined time used in the process shown in step S101 is compared with the coverage in step S104, and platinum is a platinum oxide. Whether or not it is covered only by is determined. If the coverage calculated in step S104 is greater than the coverage determined according to time, it is determined that a substance other than platinum oxide (hereinafter referred to as a contaminant substance) covers platinum together with platinum oxide. Is done.

  When it is determined that the contaminant substance covers the platinum oxide together with the platinum oxide (step S105: NO), the process proceeds to the process shown in step S110 in order to remove the contaminant substance together with the platinum oxide. On the other hand, when it is determined that platinum is covered only with platinum oxide (step S105: YES), the supply of the cathode gas to the fuel cell 10 is stopped (step S106). In the present embodiment, the control unit 90 transmits a command signal to the compressor 30 and stops the compressor 30, whereby supply of the cathode gas to the fuel cell 10 is stopped. As a result, the cathode potential of the fuel cell 10 decreases.

  Then, the cathode potential is monitored (step S107). In the present embodiment, the cathode potential is calculated from the cell voltage and monitored in order to detect that the cathode potential has dropped to the target potential determined in the process shown in step S102. In the present embodiment, the cathode potential of the fuel cell 10 is accurately controlled by calculating the cathode potential from the cell voltage and directly monitoring it. Here, the cell voltage and the cathode potential have the following relationship.

Cell voltage = cathode potential−anode potential− (current i × internal resistance R)
In general, the overvoltage on the anode side is negligibly small. Therefore, if no current flows through the fuel cell 10, the cathode potential shows the same value as the cell voltage. On the other hand, when a current flows through the fuel cell 10, the current i is detected by the current detection unit 80, and the resistance value of the fuel cell 10 detected by the resistance detection unit 60 is divided by the number of stacks of the single cells 11. The internal resistance R of the single cell 11 is calculated. Based on these values, the cathode potential is calculated from the cell voltage.

  Next, it is determined whether or not the cathode potential has reached the target potential (step S108). When the cathode potential does not reach the target potential (step S108: NO), the process waits until the cathode potential reaches the target potential.

  On the other hand, when the cathode potential reaches the target potential (step S108: YES), the supply of the cathode gas to the fuel cell 10 is resumed (step S109), and the process is terminated. In the present embodiment, the control unit 90 transmits a command signal to the compressor 30 to operate the compressor 30, whereby supply of the cathode gas to the fuel cell 10 is resumed.

  As described above, according to the processing shown in steps S106 to S109, the supply of the cathode gas to the fuel cell 10 is stopped, so that the cathode potential of the fuel cell 10 becomes 0.6 Vvs. RHE or 0.8Vvs. Temporarily lowered to the RHE target potential. As a result, the power generation performance of the fuel cell 10 is recovered by reducing platinum oxide while suppressing dissolution of platinum.

  On the other hand, in the process shown in step S105, when it is determined that platinum is covered with platinum oxide and contaminants (step S105: NO), current is taken out from the fuel cell 10 (step S110). In the present embodiment, the control unit 90 transmits a command signal to the loader 70 to operate the loader 70 and take out current from the fuel cell 10. As a result, the cathode potential decreases and water is generated as the fuel cell 10 generates power.

  Then, the cathode potential is monitored (step S111). In the present embodiment, the cathode potential is calculated from the cell voltage and monitored in order to detect that the cathode potential has decreased to the target potential calculated in the process shown in step S102. Note that the method for calculating the cathode potential from the cell voltage is the same as the processing shown in step S107, and thus detailed description thereof is omitted.

  Next, it is determined whether or not the cathode potential has reached the target potential (step S112). If the cathode potential does not reach the target potential (step S112: NO), the process waits until the cathode potential reaches the target potential.

  On the other hand, when the cathode potential reaches the target potential (step S112: YES), the extraction of the current from the fuel cell 10 is stopped (step S113), and the process is terminated. In the present embodiment, the control unit 90 transmits a command signal to the loader 70 to stop the operation of the loader 70, whereby the extraction of the current from the fuel cell 10 is stopped.

  As described above, according to the processes shown in steps S110 to S113, the cathode potential of the fuel cell 10 is 0.6 Vvs. RHE or 0.8Vvs. Temporarily lowered to the RHE target potential. As a result, the power generation performance of the fuel cell 10 is recovered by reducing platinum oxide while suppressing dissolution of platinum. In addition, contaminants are removed by the flow of water generated as the fuel cell 10 generates power.

  Next, the target potential determination process shown in step S102 of FIG. 3 will be described in detail with reference to FIG. FIG. 4 is a flowchart for explaining the target potential determination processing in the present embodiment.

  As shown in FIG. 4, in the target potential determination process of the present embodiment, first, the temperature of the fuel cell 10 is detected (step S201). In the present embodiment, the temperature of the fuel cell 10 is detected by the temperature detector 50. For example, the temperature detection unit 50 detects the temperature of the single cell 11 disposed in the vicinity of the gas discharge port of the fuel cell 10. Moreover, the temperature detection part 50 detects the temperature between a separator and a gas diffusion layer, or the temperature between a gas diffusion layer and a catalyst layer.

  Next, the water content of the fuel cell 10 is detected (step S202). In the present embodiment, the resistance value of the fuel cell 10 is detected by the resistance detector 60 and the water content is calculated. More specifically, a resistance value-water content conversion table showing the relationship between the resistance value of the fuel cell 10 and the water content is determined in advance, and the fuel cell 10 is based on the resistance value detected by the resistance detection unit 60. The water content of is calculated. Note that the resistance value of the fuel cell 10 increases as the water content decreases.

  Next, it is determined whether or not the fuel cell 10 is in a high temperature / high water content state (step S203). In the present embodiment, the fuel cell 10 is in a high temperature / high water content state based on the temperature and water content detected in the processes shown in steps S201 and S202 based on a preset conversion table as shown in FIG. It is determined whether or not.

  When it is determined that the fuel cell 10 is not in a high temperature / high water content state (step S203: NO), it is assumed that the fuel cell 10 is not easily deteriorated, so that the power generation performance of the fuel cell 10 can be quickly recovered. Target potential is 0.6Vvs. RHE is determined. On the other hand, when it is determined that the fuel cell 10 is in a high temperature / high water content state (step S203: YES), it is determined that the fuel cell 10 is likely to be deteriorated, and power generation performance is given priority to suppression of deterioration of the fuel cell. The target potential is 0.8 Vvs. RHE is determined.

  As described above, according to the processing of the flowchart shown in FIG. 4, 0.6 Vvs. RHE or 0.8Vvs. A target potential for RHE is determined. More specifically, when the fuel cell 10 is not in a high temperature / high water content state, the target potential of the cathode potential is 0.6 Vvs. So that the power generation performance of the fuel cell 10 is quickly recovered. RHE is determined. On the other hand, when the fuel cell 10 is in a high temperature / high water content state, the target potential of the cathode potential is 0.8 Vvs. So that the power generation performance of the fuel cell 10 is restored while giving priority to suppressing deterioration of the fuel cell. RHE is determined. As described above, the power generation performance of the fuel cell 10 is recovered by reducing the cathode potential of the fuel cell 10 to the target potential.

  Next, the relationship between the target potential of the cathode potential of the fuel cell and the degree of deterioration of the fuel cell will be described with reference to FIG.

  FIG. 6 is a diagram showing the relationship between the target potential of the cathode potential of the fuel cell and the degree of deterioration of the fuel cell. FIG. 6A is a diagram for explaining the process of changing the cathode potential of the fuel cell, and FIG. 6B is a diagram showing the catalyst surface area (Normalized) when the process of changing the cathode potential of the fuel cell is repeated. It is a figure which shows the decreasing degree of ECA).

  As shown in FIG. 6 (A), the cathode potential of the fuel cell is set to 0.95 Vvs. The catalyst surface area was measured by repeatedly changing between RHE and various target potentials. In FIG. 6B, the horizontal axis represents the number of cycles, and the vertical axis represents the catalyst surface area.

  As shown in FIG. 6B, when the cathode potential of the fuel cell is repeatedly changed, the catalyst surface area of the fuel cell decreases more as the target potential of the cathode potential of the fuel cell is lower. In other words, as the cathode potential of the fuel cell is lowered to a lower potential, more platinum is dissolved and the deterioration of the fuel cell proceeds. Therefore, according to the method of operating the fuel cell in the present embodiment, in order to restore the power generation performance of the fuel cell while giving priority to suppressing deterioration of the fuel cell, the cathode potential is increased to a higher target potential (for example, 0.8 Vvs). .RHE). On the other hand, in order to quickly recover the power generation performance of the fuel cell, the cathode potential is lowered to a lower target potential (for example, 0.6 V vs. RHE).

  Next, the relationship between the temperature and water content of the fuel cell and the degree of deterioration of the fuel cell will be described with reference to FIG.

  FIG. 7A is a diagram showing the relationship between the temperature of the fuel cell and the degree of deterioration of the fuel cell, and FIG. 7B is a diagram showing the relationship between the water content of the fuel cell and the degree of degradation of the fuel cell. It is. 7A and 7B, the horizontal axis is the number of cycles, and the vertical axis is the catalyst surface area. In FIG. 7B, the humidity of the gas supplied to the fuel cell is detected as the water content of the fuel cell.

  As shown in FIG. 7A, the higher the temperature of the fuel cell, the greater the reduction in the catalyst surface area of the fuel cell. In other words, the higher the temperature of the fuel cell, the more likely the fuel cell will deteriorate. Therefore, in the fuel cell operation method according to the present embodiment, when the temperature of the fuel cell is high, the cathode potential is lowered to a higher potential (0.8 V vs. RHE) to give priority to suppressing deterioration of the fuel cell. While restoring the power generation performance of the fuel cell. On the other hand, when the temperature of the fuel cell is low, the cathode potential is lowered to a lower potential (for example, 0.6 V vs. RHE) to quickly recover the power generation performance of the fuel cell.

  Further, as shown in FIG. 7B, the higher the water content of the fuel cell, the greater the reduction in the catalyst surface area of the fuel cell. In other words, the higher the water content of the fuel cell, the more likely the fuel cell will deteriorate. Therefore, in the fuel cell operating method according to the present embodiment, when the fuel cell has a high water content, the cathode potential is lowered to a higher potential (0.8 V vs. RHE) to give priority to suppression of deterioration of the fuel cell. At the same time, the power generation performance of the fuel cell is restored. On the other hand, when the water content of the fuel cell is low, the cathode potential is lowered to a lower potential (for example, 0.6 V vs. RHE) to quickly recover the power generation performance of the fuel cell.

  Next, with reference to FIG. 8, the mechanism of recovery and deterioration suppression of the power generation performance of the fuel cell according to the fuel cell operating method of the present embodiment will be described.

  FIG. 8 is a diagram for explaining a change in the state of platinum in the operation method of the fuel cell in the present embodiment. In FIG. 8, the cathode potential of the fuel cell is 0.6 Vvs. The case where it is lowered to a potential lower than RHE is shown as a comparative example.

As shown in FIG. 8B, in the comparative example, in order to restore the power generation performance of the fuel cell, the cathode potential of the fuel cell is set to 0.6 Vvs. Reduce to potential below RHE. In this case, in addition to the phenomenon in which platinum oxide (PtOx) is reduced to platinum (Pt), a phenomenon in which platinum is ionized to platinum ions (Pt ^{n +} ) is considered to occur. Therefore, in the comparative example, the catalytic activity is restored and the power generation performance of the fuel cell is restored, while the dissolution and reaggregation of platinum is promoted and the catalyst surface area is reduced. In addition, the dissolved platinum is reprecipitated inside the electrolyte membrane, causing deterioration of the electrolyte membrane. As a result, in the comparative example, although the power generation performance of the fuel cell is temporarily recovered, the performance of the fuel cell is deteriorated in the long term.

  On the other hand, as shown in FIG. 8A, in the fuel cell operation method according to the present embodiment, the cathode potential of the fuel cell is set to 0.6 Vvs. RHE or 0.8Vvs. Reduce to RHE. In this case, it is considered that a part of the platinum oxide is reduced and the remaining platinum oxide (PtOx) undergoes a state change and remains on the platinum surface as a protective coating. And it is thought that platinum oxide (PtOx) which caused the state change suppresses the dissolution of platinum and suppresses the deterioration of the fuel cell.

  As described above, according to the operation method of the fuel cell in the present embodiment, the cathode potential is 0.8 Vvs. The power generation performance of the fuel cell is restored while giving priority to suppression of deterioration of the fuel cell. On the other hand, when the fuel cell is not easily deteriorated, the cathode potential is 0.6 Vvs. The power generation performance of the fuel cell is quickly recovered by reducing to RHE. As a result, the power generation performance of the fuel cell can be recovered and the durability of the fuel cell can be improved.

  In the above-described embodiment, the target potential is determined based on the temperature and water content of the fuel cell. However, the target potential may be determined only from the temperature of the fuel cell, or the target potential may be determined only from the water content.

  In the above-described embodiment, 0.6 Vvs. Is selected depending on the temperature and water content of the fuel cell. RHE and 0.8 Vvs. One of the two potential levels of RHE was selected and determined as the target potential. However, according to the state of the fuel cell, one potential level may be selected from three or more potential levels and determined as the target potential. Such a potential level is 0.6 to 0.95 Vvs. It is preferably set within the range of RHE. Target potential is 0.6Vvs. When it is less than RHE, platinum is easily dissolved, and deterioration of the fuel cell cannot be reliably suppressed. The target potential is 0.95 Vvs. When it exceeds RHE, platinum oxide is not reduced depending on the material, and the power generation performance of the fuel cell is not recovered.

  Next, a fuel cell vehicle equipped with the fuel cell system 100 according to the present embodiment will be described with reference to FIG.

  FIG. 9 is a diagram illustrating a fuel cell vehicle equipped with the fuel cell system according to the present embodiment. The fuel cell vehicle 200 in the present embodiment is equipped with the fuel cell system 100 as a driving power source. The motor of the automobile 200 is driven by the electric power generated by the fuel cell 10, and the automobile 200 runs. As described above, even when the fuel cell vehicle 200 is involved in a traffic jam and the idling operation of the fuel cell 10 is continued for a long time, the power generation performance of the fuel cell 10 is maintained by the above-described processing. And according to the fuel cell vehicle 200 of the present embodiment, since the durability of the fuel cell 10 is improved, the reliability of the vehicle 200 is improved.

  The temperature and water content of the fuel cell vary depending on the region and season in which the fuel cell vehicle 200 is actually used. For example, the average temperature in Moscow in January is -9.5 ° C and the minimum temperature is -16.2 ° C, while the average temperature in June in New Delhi is 33.8 ° C and the maximum temperature is 39. 9 ° C. Therefore, the temperature of the fuel cell can be detected by considering the relationship between the catalyst surface area decrease curve at about −10 ° C. indicated by the broken line in FIG. 7A and the catalyst surface area decrease curve corresponding to 30 ° C. or 50 ° C. Thus, by determining the target potential of the cathode potential of the fuel cell, an effect of suppressing the reduction of the catalyst surface area by about 30% is expected.

  Further, the humidity (RH) in the desert region is 20 to 30%, whereas the humidity in the rainy season in Southeast Asia is 80 to 90%. Therefore, in consideration of the relationship between the water content and the catalyst surface area shown in FIG. 7B, the target potential of the cathode potential of the fuel cell is determined by detecting the water content of the fuel cell. Expected to reduce surface area.

  As described above, the described embodiment has the following effects.

  (A) The fuel cell system of the present embodiment includes a fuel cell, a temperature detector, a resistance detector, a compressor, a loader, and a controller. The fuel cell contains platinum as an electrode catalyst. The temperature detector and the resistance detector detect the temperature and water content of the fuel cell. The control unit determines a target potential that is a target value of the cathode potential of the fuel cell based on the detected state of the fuel cell. The compressor, the loader, and the control unit recover the power generation performance of the fuel cell by lowering the cathode potential of the fuel cell to the determined target potential. Accordingly, since the target potential of the cathode potential that is lowered to restore the power generation performance of the fuel cell is changed according to the state of the fuel cell, platinum oxide can be reduced while suppressing the dissolution of platinum. . As a result, the power generation performance of the fuel cell can be recovered and the durability of the fuel cell can be improved.

  (B) The control unit determines the target potential based on the state of the fuel cell so that the target potential becomes higher as the fuel cell is more likely to deteriorate. Therefore, as the fuel cell is more likely to be deteriorated, the power generation performance is recovered by giving priority to the suppression of deterioration of the fuel cell, so that the durability of the fuel cell can be reliably improved.

  (C) The control unit is 0.6Vvs. One potential level corresponding to the state of the fuel cell is selected from two potential levels set in advance in a range equal to or higher than RHE, and determined as a target potential. Therefore, the power generation performance of the fuel cell can be recovered and the durability of the fuel cell can be further improved.

  (D) The control unit determines a higher target potential, assuming that the fuel cell is more likely to deteriorate as the temperature of the fuel cell increases. Therefore, the durability of the fuel cell can be improved by detecting the temperature of the fuel cell.

  (E) The control unit determines a higher target potential on the assumption that the fuel cell is more likely to deteriorate as the water content of the fuel cell increases. Therefore, the durability of the fuel cell can be improved by detecting the water content of the fuel cell.

  (F) The fuel cell vehicle of the present embodiment is equipped with the fuel cell system as a driving power source. Therefore, since the durability of the fuel cell is improved, the reliability of the fuel cell vehicle is improved.

  (G) The fuel cell operating method in the present embodiment includes a state detection stage, a potential determination stage, and a potential control stage. In the state detection step, the state of the fuel cell containing platinum as an electrode catalyst is detected. In the potential determination step, a target potential that is a target value of the cathode potential of the fuel cell is determined based on the detected state of the fuel cell. In the potential control stage, the power generation performance of the fuel cell is restored by lowering the cathode potential of the fuel cell to the determined target potential. Accordingly, since the target potential of the cathode potential that is lowered to restore the power generation performance of the fuel cell is changed according to the state of the fuel cell, platinum oxide can be reduced while suppressing the dissolution of platinum. . As a result, the power generation performance of the fuel cell can be recovered and the durability of the fuel cell can be improved.

(Second Embodiment)
In the first embodiment, the target potential of the cathode potential is determined from the temperature and water content of the fuel cell. In the present embodiment, the target potential is determined from the history of the cathode potential of the fuel cell.

  FIG. 10 is a flowchart for explaining target potential determination processing according to the second embodiment of the present invention. Except for the target potential determination process, the configuration of the fuel cell system according to the present embodiment is the same as the configuration according to the first embodiment, and thus detailed description thereof is omitted.

  As shown in FIG. 10, in the target potential determination process of the present embodiment, first, the history of the cathode potential of the fuel cell 10 is acquired (step S301). In the present embodiment, the cathode potential history of the fuel cell 10 is stored in a storage unit (not shown), and the cathode potential history data from the start of processing to a predetermined time before is acquired.

  Next, in the cathode potential history data, it is determined whether or not there is a period during which the cathode potential has become a predetermined value or less (step S302). Here, the predetermined value is a potential for determining that the fuel cell 10 is in a high-load operation state. If there is no period in which the cathode potential is equal to or lower than the predetermined value (step S302: NO), the process proceeds to step S305 and subsequent steps. On the other hand, when there is a period in which the cathode potential is equal to or lower than the predetermined value (step S302: YES), it is determined whether or not the period in which the cathode potential is lower than the predetermined value is equal to or longer than a predetermined time (step S303).

  When the period during which the cathode potential is less than or equal to the predetermined value is less than the predetermined time (step S303: NO), the process proceeds to step S305 and subsequent steps. On the other hand, when the period during which the cathode potential is equal to or lower than the predetermined value is longer than the predetermined time (step S303: YES), the target potential is set to 0.8 Vvs. RHE is determined (step S304), and the process is terminated.

  On the other hand, when there is no period in which the cathode potential is less than or equal to a predetermined value (step S302: NO), or when the period in which the cathode potential is less than or equal to the predetermined value is less than a predetermined time (step S303: NO), the cathode potential is a predetermined potential width. It is determined whether or not there is a portion that has changed as described above (step S305). Here, the predetermined potential range is a potential range for determining that the operating state of the fuel cell has greatly changed from the high load operating state to the low load operating state or from the low load operating state to the high load operating state. is there. If there is no portion where the cathode potential fluctuates by more than the predetermined potential width (step S305: NO), the target potential is 0.6 Vvs. RHE is determined (step S306), and the process is terminated.

  On the other hand, if there is a location where the cathode potential has fluctuated by a predetermined potential width or more (step S305: YES), whether or not the number of locations in which the cathode potential has fluctuated by a predetermined potential width or more in the cathode potential history data is greater than a predetermined number. Is determined (step S307). When the number of locations where the cathode potential fluctuates by more than a predetermined potential width is greater than or equal to the predetermined number (step S307: YES), the target potential is 0.8 Vvs. RHE is determined (step S304), and the process is terminated. On the other hand, when the number of locations where the cathode potential fluctuates by more than a predetermined potential width is less than the predetermined number (step S307: NO), the target potential is 0.6 Vvs. RHE is determined (step S306), and the process is terminated.

  As described above, according to the process of the flowchart shown in FIG. 10, based on the history of the cathode potential of the fuel cell 10, 0.6 Vvs. RHE or 0.8Vvs. A target potential for RHE is determined. More specifically, when the period during which the cathode potential of the fuel cell is less than or equal to a predetermined value is short, or when the number of fluctuations of the cathode potential more than a predetermined potential width is small, the power generation performance of the fuel cell is quickly recovered. The target potential of the cathode potential is 0.6 Vvs. RHE is determined. On the other hand, if the period during which the cathode potential of the fuel cell is less than or equal to the predetermined value is long, or if the number of fluctuations of the cathode potential is greater than or equal to the predetermined potential width, the power generation performance of the fuel cell is restored while giving priority to suppressing deterioration of the fuel cell. As shown, the target potential of the cathode potential is 0.8 Vvs. RHE is determined. According to the operation method of the fuel cell having such a configuration, the power generation performance of the fuel cell can be recovered and the durability of the fuel cell can be improved.

  As described above, the present embodiment described has the following effects in addition to the effects of the first embodiment.

  (H) The control unit is in a state where the fuel cell is more likely to be deteriorated as the period during which the cathode potential of the fuel cell is less than or equal to a predetermined value is longer or the number of fluctuations of the cathode potential of the fuel cell is greater than or equal to a predetermined potential width. As described above, a high target potential is determined. Therefore, the durability of the fuel cell can be improved by detecting the history of the cathode potential of the fuel cell.

(Third embodiment)
In the present embodiment, the target potential is determined from the history of the accelerator opening of the fuel cell vehicle on which the fuel cell is mounted.

  FIG. 11 is a flowchart for explaining target potential determination processing according to the third embodiment of the present invention. Except for the target potential determination process, the configuration of the fuel cell system according to the present embodiment is the same as the configuration according to the first embodiment, and thus detailed description thereof is omitted.

  As shown in FIG. 11, in the target potential determination process of the present embodiment, first, the history of the accelerator opening of the fuel cell vehicle 200 is acquired (step S401). In the present embodiment, the history of the accelerator opening of the fuel cell vehicle 200 is stored in a storage unit (not shown), and history data of the accelerator opening from the processing start time to a predetermined time before is acquired.

  Next, it is determined whether or not there is a period in which the accelerator opening is equal to or greater than a predetermined value in the history data of the accelerator opening (step S402). Here, the predetermined value is an accelerator opening for determining that the fuel cell is in a high-load operation state. When there is no period in which the accelerator opening is equal to or greater than the predetermined value (step S402: NO), the target potential is 0.6 Vvs. RHE is determined (step S403), and the process is terminated.

  On the other hand, when there is a period during which the accelerator opening is equal to or greater than the predetermined value (step S402: YES), it is determined whether or not the period during which the accelerator opening is equal to or greater than the predetermined value is equal to or greater than a predetermined time (step S404). When the period during which the accelerator opening is equal to or greater than the predetermined value is less than the predetermined time (step S404: NO), the target potential is 0.6 Vvs. RHE is determined (step S403), and the process is terminated.

  When the period during which the accelerator opening is equal to or greater than the predetermined value is equal to or greater than the predetermined time (step S404: YES), the target potential is set to 0.8 Vvs. RHE is determined (step S405), and the process is terminated.

  As described above, according to the processing of the flowchart shown in FIG. 11, 0.6 V vs. V is based on the accelerator opening of the fuel cell vehicle 200 on which the fuel cell 10 is mounted. RHE or 0.8Vvs. A target potential for RHE is determined. More specifically, when the time period during which the accelerator opening of the fuel cell is greater than or equal to a predetermined value is short, the target potential of the cathode potential is 0.6 V vs. so that the power generation performance of the fuel cell can be quickly recovered. RHE is determined. On the other hand, when the time period during which the accelerator opening of the fuel cell is greater than or equal to a predetermined value is long, the target potential of the cathode potential is 0.8 Vvs. So that the power generation performance of the fuel cell is restored while giving priority to suppressing deterioration of the fuel cell. RHE is determined. According to the operation method of the fuel cell having such a configuration, the power generation performance of the fuel cell can be recovered and the durability of the fuel cell can be improved.

  As described above, the described embodiment has the following effects in addition to the effects of the first and second embodiments.

  (I) The control unit determines a higher target potential, assuming that the fuel cell is more likely to deteriorate as the period during which the accelerator opening is equal to or greater than a predetermined value is longer. Therefore, the durability of the fuel cell can be improved by detecting the history of the accelerator opening of the fuel cell vehicle.

  As described above, in the first to third embodiments described, the fuel cell system, the fuel cell operating method, and the fuel cell vehicle of the present invention have been described. However, it goes without saying that the present invention can be appropriately added, modified, and omitted by those skilled in the art within the scope of the technical idea.

  For example, in the first to third embodiments described above, the cathode potential of the fuel cell is lowered to the target potential by stopping the supply of the cathode gas to the fuel cell or by taking out the current from the fuel cell. I let you. However, as a method for reducing the cathode potential of the fuel cell, various methods such as flooding, supply of a reducing agent, short-circuit between the anode and the cathode, or depressurization of the cathode gas can be used. In the flooding process, a state in which no gas flows is created by lowering the temperature of the fuel cell, supplying a highly humidified gas, or supplying liquid water, thereby lowering the cathode potential. In the supply process of the reducing agent, the cathode potential is lowered by supplying a gas containing an oxidizing agent such as hydrogen, hydrogen peroxide, hydrazine, ascorbic acid, and citric acid to the fuel cell.

It is a figure which shows schematic structure of the fuel cell system in the 1st Embodiment of this invention. It is a perspective view which shows the cell structure of the fuel cell in the fuel cell system shown in FIG. 2 is a flowchart for explaining a method of operating a fuel cell by the fuel cell system shown in FIG. It is a flowchart for demonstrating the target electric potential determination process shown to step S102 of FIG. FIG. 5 is a diagram for explaining processing for determining whether or not the fuel cell is in a high temperature / high water content state in the target potential determination processing shown in FIG. 4. It is a figure which shows the relationship between the target electric potential in the fuel cell system shown in FIG. 1, and the deterioration degree of a fuel cell. FIG. 2 is a diagram showing the relationship between the temperature and water content of the fuel cell and the degree of deterioration of the fuel cell in the fuel cell system shown in FIG. 1. It is a figure for demonstrating the state change of platinum in the operating method of the fuel cell shown in FIG. It is a figure explaining the fuel cell vehicle carrying the fuel cell system shown in FIG. It is a flowchart for demonstrating the target electric potential determination process in the 2nd Embodiment of this invention. It is a flowchart for demonstrating the target electric potential determination process in the 3rd Embodiment of this invention.

Explanation of symbols

10 Fuel cell,
20 Fuel tank,
30 compressor (potential control means),
40 voltage detector,
50 temperature detector (state detection means),
60 resistance detection unit (state detection means),
70 loader (potential control means),
80 current detector,
90 control unit (potential control means and potential determination means),
100 fuel cell system,
200 Fuel cell vehicle.

Claims (9)

A fuel cell containing platinum as an electrode catalyst;
State detecting means for detecting the state of the fuel cell;
A potential determining means for determining a target potential which is a target value of the air electrode potential of the fuel cell based on the detected state of the fuel cell;
A potential control means for recovering the power generation performance of the fuel cell by reducing the air electrode potential of the fuel cell to the determined target potential;
A fuel cell system comprising:   The said potential determination means determines the said target potential based on the state of the said fuel cell so that the said target potential becomes so high that the said fuel cell is in the state which is easy to deteriorate. Fuel cell system.   The potential determining means selects one potential level corresponding to the state of the fuel cell from a plurality of potential levels preset in a range of 0.6 V or more with respect to the reversible hydrogen electrode potential, The fuel cell system according to claim 2, wherein the fuel cell system is determined as a target potential. The state detection means has temperature detection means for detecting the temperature of the fuel cell,
3. The fuel cell system according to claim 2, wherein the potential determination unit determines the higher target potential on the assumption that the fuel cell is more likely to deteriorate as the detected temperature is higher. The state detection means includes water content detection means for detecting the water content of the fuel cell,
3. The fuel cell system according to claim 2, wherein the potential determination unit determines the higher target potential, assuming that the fuel cell is more likely to deteriorate as the detected water content increases. The state detection means has a potential history detection means for detecting a history of the air electrode potential of the fuel cell,
The potential determining means is in a state in which the fuel cell is more likely to deteriorate as the period during which the air electrode potential of the fuel cell is less than or equal to a predetermined value is longer or the number of fluctuations of the air electrode potential is greater than or equal to a predetermined potential width. The fuel cell system according to claim 2, wherein the target potential that is high is determined. The state detecting means includes accelerator opening history detecting means for detecting a history of accelerator opening of a fuel cell vehicle equipped with the fuel cell,
The said electric potential determination means determines the said high target electric potential as the said fuel cell is in the state which is easy to deteriorate, so that the period when the said accelerator opening is more than predetermined value is long. Fuel cell system.   A fuel cell vehicle comprising the fuel cell system according to any one of claims 1 to 7 as a driving power source. Detecting a state of a fuel cell containing platinum as an electrode catalyst;
Determining a target potential that is a target value of the air electrode potential of the fuel cell based on the detected state of the fuel cell;
Recovering the power generation performance of the fuel cell by reducing the cathode potential of the fuel cell to the determined target potential;
A method of operating a fuel cell, comprising:

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