Water electrolysis device and method for controlling water electrolysis cell

Abstract

To provide a water electrolysis device capable of suppressing elution of a metal catalyst of an anode electrode and a method for controlling a water electrolysis cell.SOLUTION: According to an embodiment, a water electrolysis device comprises a water electrolysis cell, a power supply unit, and a control unit. The water electrolysis cell applies electrolysis to water supplied to an anode electrode using a solid polymer electrolyte membrane in which the anode electrode is installed on one surface and a cathode electrode is installed on the other surface to generate hydrogen and oxygen. The power supply unit can change electric potential of the anode electrode. In a first mode, the control unit controls the power supply unit so that the electric potential of the anode electrode becomes higher than or equal to first electric potential. In a second mode, the control unit controls the state of the water electrolysis cell so that the electric potential of the anode electrode becomes lower than the first electric potential and higher than or equal to elution potential of a prescribed catalyst in the anode electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a water electrolysis device and a method for controlling a water electrolysis cell. [Background technology]

[0002] A water electrolysis device is a device that generates hydrogen and oxygen. During operation, an external direct current is passed through the water electrolysis cell included in the water electrolysis device, electrolyzing water to generate hydrogen from the cathode electrode and oxygen from the anode electrode. Water electrolysis cells include polymer electrolyte membrane (PEM) water electrolysis cells, which use a polymer electrolyte membrane as a diaphragm, alkaline water electrolysis cells, which have a diaphragm in an alkaline electrolyte, and solid oxide water electrolysis cells, which use a solid oxide as an electrolyte. Among these, polymer electrolyte water electrolysis cells have a low operating temperature and are capable of generating highly pure hydrogen. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-99905 Summary of the Invention [Problem to be solved by the invention]

[0004] However, it has been found that when operation is stopped, metals are eluted during the oxidation-reduction reaction process of the metal catalyst in the anode electrode of a solid polymer water electrolysis cell. The elution of metals during the oxidation-reduction reaction process of the catalyst may deteriorate the performance of the anode catalyst, which may result in a deterioration in the performance of the water electrolysis cell.

[0005] Therefore, an object of the present invention is to provide a water electrolysis apparatus and a method for controlling a water electrolysis cell that can suppress elution of a metal catalyst from an anode electrode. [Means for solving the problem]

[0006] According to this embodiment, the water electrolysis device includes a water electrolysis cell, a power supply unit, and a control unit. The water electrolysis cell uses a solid polymer electrolyte membrane having an anode electrode on one side and a cathode electrode on the other side to electrolyze water supplied to the anode electrode to generate hydrogen and oxygen. The power supply unit is capable of changing the potential of the anode electrode. In a first mode, the control unit controls the power supply unit so that the potential of the anode electrode is equal to or higher than a first potential, and in a second mode, controls the state of the water electrolysis cell so that the potential of the anode electrode is lower than the first potential and equal to or higher than the elution potential of a predetermined metal catalyst at the anode electrode. [Effects of the Invention]

[0007] According to the present invention, it is possible to suppress the elution of the metal catalyst from the anode electrode. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a block diagram showing the configuration of a water electrolysis device. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of a unit cell that constitutes a water electrolysis cell. [Figure 3] FIG. 2 is a block diagram showing an example of the configuration of a power supply unit. [Figure 4] FIG. 2 is a block diagram showing an example of the configuration of a control unit. [Figure 5] FIG. 10 is a diagram showing a control example as a comparative example of the control unit. [Figure 6] FIG. 3 is a diagram schematically illustrating a reaction between an anode electrode and a cathode electrode. [Figure 7] FIG. 10 is a diagram showing a reaction when stopped. [Figure 8] A diagram showing the reaction after 2 minutes have passed since the test was stopped. [Figure 9] FIG. 4 is a diagram showing a control example of a control unit. [Figure 10] 4 is a flowchart showing an example of control performed by the control unit on the water electrolysis cell. [Figure 11] FIG. 4 is a block diagram showing the configuration of a water electrolysis apparatus according to a second embodiment. [Figure 12]FIG. 10 is a block diagram showing the configuration of a control unit according to a second embodiment. [Figure 13] FIG. 10 is a diagram showing a control example of a control unit according to the second embodiment. [Figure 14] FIG. 10 is a block diagram showing the configuration of a water electrolysis apparatus according to a third embodiment. [Figure 15] FIG. 10 is a diagram showing an example of the configuration of a unit cell according to a third embodiment. [Figure 16] FIG. 10 is a block diagram showing the configuration of a control unit according to a third embodiment. [Figure 17] FIG. 11 is a diagram showing a control example of a control unit according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] A water electrolysis apparatus and a method for controlling a water electrolysis cell according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that the embodiment described below is merely an example of an embodiment of the present invention, and the present invention should not be construed as being limited to these embodiments. Furthermore, in the drawings referred to in this embodiment, identical parts or parts having similar functions are denoted by the same or similar reference numerals, and repeated description thereof may be omitted. Furthermore, for convenience of explanation, the dimensional proportions in the drawings may differ from the actual proportions, and some components may be omitted from the drawings.

[0010] (First embodiment) Fig. 1 is a block diagram showing the configuration of a water electrolysis apparatus 10a according to a first embodiment. As shown in Fig. 1, the water electrolysis apparatus 10a according to this embodiment is an example of a water electrolysis apparatus that generates hydrogen and oxygen using a solid polymer electrolyte membrane. The water electrolysis apparatus 10a includes a water electrolysis cell 20a, a first water inlet manifold 21, a second water outlet manifold 22, a gas-liquid separator 23, a first circulation pump 24, a water tank 26, a hydrogen manifold 27, a hydrogen-gas-liquid separator 28, a dehumidifier 29, a power supply unit 30, and a control unit 40.

[0011] FIG. 2 is a diagram showing an example of the configuration of a unit cell 100a constituting the water electrolysis cell 20a. As shown in FIG. 2, the unit cell 100a includes a polymer electrolyte membrane (PEM) electrolyte membrane 101, an anode electrode 102, a cathode electrode 104, an anode current collector 106, and a cathode current collector 108. In the unit cell 100a, the solid polymer electrolyte membrane 101 is sandwiched between the anode electrode 102 and the cathode electrode 104, and the anode current collector 106 and the cathode current collector 108 are disposed on both outer sides of the solid polymer electrolyte membrane 101. The water electrolysis cell 20a is configured by stacking a plurality of the unit cells 100a. Note that the water electrolysis cell 20a according to this embodiment is configured by stacking a plurality of the unit cells 100a in series, but is not limited to this. For example, the water electrolysis cell 20a may be configured by the unit cells 100a. Alternatively, a plurality of unit cells 100a may be connected in parallel to form a water electrolysis cell 20a.

[0012] The solid polymer electrolyte membrane 101 is made of, for example, a fluorine-based polymer having sulfonic acid groups. The anode electrode 102 is made of, for example, an iridium oxide catalyst (IrOx) supported on titanium nonwoven fabric. The cathode electrode 104 is made of, for example, a mixture of a platinum-supported carbon catalyst or a platinum alloy-supported carbon catalyst and an ionomer, coated on carbon paper, carbon cloth, carbon nonwoven fabric, or titanium nonwoven fabric.

[0013] The anode current collector 106 is connected to the anode of the power supply unit 30, and the cathode current collector 108 is connected to the cathode of the power supply unit 30. This causes hydrogen ions to move within the solid polymer electrolyte membrane 101, electrolyzing the water H2O supplied from the supply unit G2. At this time, the anode electrode 102 converts 2H2O to 4H + +4e - The reaction +O2 occurs, and oxygen O2 and unreacted water H2O are discharged from outlet G4.

[0014] On the other hand, the cathode electrode 104 is + +4e -The reaction 2H2O → 2H2 + O2 occurs, and hydrogen H2 is discharged from the discharge part G6. In this way, the reaction 2H2O → 2H2 + O2 occurs within the unit cell 100a.

[0015] The first water inlet manifold 21 connects the gas-liquid separator 23 with the supply section G2 of each unit cell 100a, so that the first water inlet manifold 21 supplies water from the gas-liquid separator 23 to the supply section G2 of each unit cell 100a.

[0016] The second water outlet manifold 22 connects the gas-liquid separator 23 with the discharge section G4 of each unit cell 100a, thereby supplying the oxygen-containing water discharged from the discharge section G4 of each unit cell 100a to the gas-liquid separator 23.

[0017] The gas-liquid separator 23 collects oxygen-containing water discharged from the discharge section G4 of each unit cell 100a and separates the oxygen from the water. The first circulation pump 24 supplies the oxygen-containing water discharged from the discharge section G4 of each unit cell 100a to the gas-liquid separator 23 via the second water outlet manifold 22. The first circulation pump 24 also supplies the water from which oxygen has been separated, supplied from the gas-liquid separator 23, to the supply section G2 of each unit cell 100a via the first water inlet manifold 21.

[0018] The gas-liquid separator 23 is further connected to a water tank 26 via a pump 25. The water tank 26 temporarily stores pure water supplied from the outside. The pump 25 supplies pure water from the water tank 26 to the gas-liquid separator 23 when the water electrolysis apparatus 10a is in operation.

[0019] The hydrogen manifold 27 connects the hydrogen gas-liquid separator 28 with the discharge section G6 of each unit cell 100a. As a result, the hydrogen manifold 27 supplies the hydrogen gas and water discharged from the discharge section G6 of each unit cell 100a to the hydrogen gas-liquid separator 28.

[0020] The hydrogen gas-liquid separator 28 separates the hydrogen gas from the water. The hydrogen gas-liquid separator 28 is further connected to a dehumidifier 29.

[0021] The dehumidifier 29 is capable of removing water vapor, which is an impurity, from the hydrogen gas discharged from the hydrogen gas-liquid separator 28. The hydrogen gas from which the water vapor has been removed by the dehumidifier 29 is supplied to a hydrogen consuming device, such as a fuel cell.

[0022] Fig. 3 is a block diagram showing an example configuration of the power supply unit 30. As shown in Fig. 3, the power supply unit 30 includes a DC power supply 30a capable of varying the supply voltage, a plurality of switches T10, T12, and T14, and a voltmeter V10. The anode of the DC power supply 30a is connected to an anode current collector 106, and the cathode is connected to a cathode current collector 108 via switch T10. The cathode of the DC power supply 30a can be connected to a ground potential via switch T12. Similarly, the cathode current collector 108 can also be connected to a ground potential via switch T14.

[0023] The DC power supply 30a and the multiple switches T10, T12, and T14 are controlled by the control unit 40. When multiple unit cells 100a are connected in series, the value obtained by dividing the potential of the voltmeter V10 by the number of unit cells 100a is the potential between the anode current collector 106 and the cathode current collector 108 of each unit cell 100a.

[0024] Fig. 4 is a block diagram showing an example configuration of the control unit 40. As shown in Fig. 4, the control unit 40 controls the entire water electrolysis apparatus 10a and includes, for example, a storage unit 400, an acquisition unit 402, a connection control unit 404, and a voltage control unit 406. The control unit 40 includes, for example, a CPU (Central Processing Unit) and an MPU (Microprocessor), and configures each processing unit by executing a control program stored in the storage unit 400. Note that each processing unit may also be configured using an electronic circuit.

[0025] The specific configuration of the control unit 40 is not limited, and may be, for example, a field programmable gate array (FPGA) or other devices such as an application specific integrated circuit (ASIC). Alternatively, the control unit 40 may be configured by a general-purpose computer.

[0026] The storage unit 400 is configured by, for example, an HDD (hard disk drive), an SSD (solid state drive), etc. As described above, the storage unit 400 stores the control program, a table L10 (see FIG. 5) showing the relationship between the pH (PH) of various metals and the elution potential, which will be described later with reference to FIG. 5, and the like.

[0027] The acquisition unit 402 acquires information relating to the control of the water electrolysis apparatus 10a. In this embodiment, for example, at least information relating to the voltage of the voltmeter V10 (see FIG. 3) is acquired.

[0028] The connection control unit 404 controls the connection states of the multiple switches T10, T12, and T14. The voltage control unit 406 controls the voltage of the DC power supply 30a, and controls the potential applied to the anode current collector 106 of the single cell 100a (see FIG. 2). In this way, the DC power supply 30a can change the potential applied to the anode current collector 106 under the control of the voltage control unit 406.

[0029] FIG. 5 is a diagram showing a comparative example of control by the control unit 40. The left diagram shows the thermodynamic stability of iridium oxide. The vertical axis shows the potential of the anode current collector 106 relative to hydrogen, and the horizontal axis shows the pH (PH), which is the hydrogen ion concentration of the anode electrode 102. Line L10 shows example values ​​in a table showing the relationship between the pH of iridium oxide and the elution potential. As described above, these example values ​​are stored in the memory unit 400. In this embodiment, 0 volts relative to hydrogen refers to the potential at which the separation and synthesis of hydrogen molecules and hydrogen ions are in equilibrium. Therefore, in this embodiment, when referring to a potential relative to hydrogen, it refers to the potential at 0 volts at which the separation and synthesis of hydrogen molecules and hydrogen ions are in equilibrium.

[0030] In this embodiment, a state in which the potential of the anode electrode 102 of the unit cell 100a is controlled to be equal to or higher than a first potential relative to a hydrogen reference for the purpose of hydrogen generation is referred to as a first mode (operating mode). For example, the first potential is 1.8 volts relative to a hydrogen reference. In this embodiment, the potential of the anode electrode 102 of the unit cell 100a relative to a hydrogen reference is approximately equal to the potential between the anode current collector 106 and the cathode current collector 108. Therefore, in the first mode, 1.8 volts is applied between the anode current collector 106 and the cathode current collector 108 of the unit cell 100a.

[0031] 5, in state St10 of the first mode (operating mode), the connection control unit 404 turns on the switch T10 and turns off the switches T12 and T14. The voltage control unit 406 controls the voltage of the DC power supply 30a so that the potential between the anode current collector 106 and the cathode current collector 108 of the single cell 100a becomes, for example, 1.8 volts.

[0032] 6 is a diagram schematically illustrating the reaction between the anode electrode 102 and the cathode electrode 104 in state St10 of the first mode (operating mode). During operation (St10), as described above, the reaction 2H2O → 2H2 + O2 occurs within the unit cell 100a.

[0033] As shown in Figure 5 again, during shutdown (St12), the voltage control unit 406 controls the voltage of the DC power supply 30a so that the potential applied between the anode current collector 106 and the cathode current collector 108 of the single cell 100a becomes zero.

[0034] 7 is a diagram showing a schematic diagram of the reaction between the anode electrode 102 and the cathode electrode 104 during the shutdown (St12). During the shutdown (St12), a so-called fuel cell reaction occurs, and the anode electrode 102 reacts with O2 + 4H + +4e - On the other hand, at the cathode electrode 104, the reaction 2H2 → 4H + +4e - The reaction occurs.

[0035] FIG. 8 is a diagram showing a schematic diagram of the reaction between the anode electrode 102 and the cathode electrode 104 when hydrogen leaks (St14) after a certain time has passed since the shutdown (St12). As time passes from the shutdown (St12), oxygen in the anode electrode 102 is gradually consumed, and excess hydrogen causes the potential of the anode electrode 102 to drop to 0 V. However, when the pH is 0 (pH=0), iridium oxide is reduced to iridium when the pH drops below 1 volt. Even if the switch T10 is disconnected, hydrogen is supplied via the solid polymer electrolyte membrane 101, so the potential of the anode electrode 102 drops to 0 V.

[0036] 5, as shown in the right diagram of Fig. 5, the catalyst of the anode electrode that was reduced to iridium during hydrogen leakage (St14) is oxidized when the potential again exceeds 1 V during operation (St10). In this way, repeated oxidation-reduction reactions of the catalyst containing iridium oxide in the anode electrode 102 cause the elution of iridium, degrading the performance of the anode catalyst in the anode electrode 102 and degrading the performance of the water electrolysis cell 20a.

[0037] 9 is a diagram showing an example of control by the control unit 40 according to this embodiment. The left diagram shows the thermodynamic stability of iridium oxide. The vertical axis represents the potential of the anode current collector 106, and the horizontal axis represents the pH (PH), which is the hydrogen ion concentration of the anode electrode 102.

[0038] In this embodiment, the state in which the potential of the anode electrode 102 is controlled to be lower than the first potential relative to the hydrogen reference and equal to or higher than the elution potential of a predetermined metal is referred to as the second mode (stop mode). For example, if the catalyst of the anode electrode 102 contains iridium oxide, the second mode is a state in which the potential of the anode electrode 102 is controlled to be lower than the first voltage relative to the hydrogen reference and equal to or higher than the elution potential of iridium oxide, for example, to stop hydrogen generation.

[0039] In this embodiment, the control unit 40 controls the water electrolysis cell 20a to a state St10 of the first mode (operating mode), and then controls the water electrolysis cell 20a to a state St16 of the second mode (stopping mode). As described above, the potential between the anode current collector 106 and the cathode current collector 108 is equivalent to the hydrogen reference potential. Therefore, in the second mode (stop mode), the connection control unit 404 may apply the second potential between the anode current collector 106 and the cathode current collector 108 of the unit cell 100a by bringing the switch T10 into a conductive state and maintaining the switches T12 and T14 in a non-conductive state.

[0040] Fig. 10 is a flowchart showing an example of control of the water electrolysis cell 20a by the control unit 40 according to this embodiment. As shown in Fig. 10, first, the control unit 40 controls the first circulation pump 24 to supply water from which oxygen has been separated, supplied from the gas-liquid separator 23, to the supply unit G2 of each unit cell 100a via the first water inlet manifold 21. Next, the connection control unit 404 turns on the switch T10 and turns off the switches T12 and T14. Then, the voltage control unit 406 controls the voltage of the DC power supply 30a so that the potential between the anode current collector 106 and the cathode current collector 108 of each unit cell 100a becomes, for example, 1.8 volts, thereby starting the first mode (step S100).

[0041] Next, the control unit 40 determines whether or not to stop the first mode (step S102), and if it is determined not to stop the first mode (NO in step S102), the control unit 40 repeats the process from step S100.

[0042] On the other hand, if it is determined that the pump should be stopped (YES in step S102), the voltage control unit 406 controls the voltage of the DC power supply 30a so that the potential of the anode current collector 106 of the single cell 100a is equal to or higher than the dissolution potential, for example, the hydrogen reference potential is equal to or higher than 1.0 V. Subsequently, the control unit 40 stops the first circulation pump 24 and starts the second mode (step S104).

[0043] Next, the control unit 40 determines whether or not to stop operation (step S106), and if it determines to stop operation (YES in step S106), it stops operation. On the other hand, if it determines not to stop operation (NO in step S106), it determines whether or not to resume the first mode (step S102), and if it determines to resume the first mode (YES in step S108), it repeats the processing from step S100. On the other hand, if it determines not to resume the first mode (NO in step S108), it repeats the processing from step S104.

[0044] As described above, according to this embodiment, in the first mode, the power supply unit 30 is controlled so that the potential of the anode electrode 102 is equal to or higher than a first potential (e.g., 1.8 volts) relative to a hydrogen reference, and in the second mode, the state of the water electrolysis cell 20a is controlled so that the potential of the anode electrode 102 is lower than the first potential (e.g., 1.8 volts) relative to a hydrogen reference and equal to or higher than an iridium elution potential (e.g., 1.0 volt). This makes it possible to suppress the oxidation-reduction reaction of iridium oxide, which is the metal catalyst of the anode electrode 102, and to suppress iridium elution, even when hydrogen production is suppressed or stopped in the second mode.

[0045] (Second embodiment) The water electrolysis apparatus 10b according to the second embodiment differs from the first embodiment in that, in the second mode, an inert gas is supplied to the cathode electrode 104 to control the potential of the anode electrode 102 to be equal to or higher than the elution potential of iridium. The differences from the water electrolysis apparatus 10a according to the first embodiment are described below.

[0046] 11 is a block diagram showing the configuration of a water electrolysis apparatus 10b according to the second embodiment. As shown in this Figure, the water electrolysis apparatus 10b according to this embodiment further includes an inert gas supply unit 50.

[0047] The inert gas supply unit 50 supplies an inert gas under the control of the control unit 40. The inert gas supply unit 50 is, for example, a nitrogen cylinder. In this case, nitrogen is supplied as the inert gas. The inert gas is not limited to nitrogen, and may be another inert gas such as argon.

[0048] The inert gas manifold 52 connects the cathode electrode 104 of each unit cell 100a (see FIG. 2) to the inert gas supply unit 50. As a result, the inert gas supply unit 50 supplies inert gas to the cathode electrode 104 of each unit cell 100a (see FIG. 2) via the inert gas manifold 52.

[0049] 12 is a block diagram showing the configuration of the control unit 40 according to the second embodiment. As shown in this figure, the control unit 40 according to this embodiment further includes a gas control unit 408.

[0050] FIG. 13 is a diagram showing an example of control by the control unit 40 according to the second embodiment. The vertical axis represents potential relative to a hydrogen reference, and the horizontal axis represents time. As shown in FIG. 13, the control unit 40 performs control in the first mode for time T10, and then performs control in the second mode for time T12. In the first mode, the gas control unit 408 performs control to stop the supply of inert gas from the inert gas supply unit 50. On the other hand, in the second mode, the gas control unit 408 performs control to supply inert gas from the inert gas supply unit 50 to the cathode electrode 104 of each single cell 100a (see FIG. 2).

[0051] In the second mode, when the supply of inert gas to the cathode electrode 104 of each unit cell 100a (see FIG. 2) begins, the potential L12 of the cathode electrode 104 begins to rise and stabilizes at a potential of about 1 volt. On the other hand, when the second mode begins, the potential L14 of the anode electrode 102 begins to decrease and stops decreasing when it reaches the same potential as the cathode electrode 104.

[0052] In the second mode, a DC potential may be applied from the DC power supply 30a. For example, if the potential increase of the cathode electrode 104 due to the inert gas does not reach 1 volt, a potential difference of 1 volt may be applied from the DC power supply 30a to the cathode electrode 104. In this case, the connection control unit 404 may apply a second potential between the anode current collector 106 and the cathode current collector 108 of the single cell 100a by placing the switch T10 in a conductive state and the switches T12 and T14 in a non-conductive state. For example, if the potential increase of the cathode electrode 104 due to the inert gas is 0.8 volts, the DC power supply 30a may apply 0.2 volts or more to the cathode electrode 104. This stabilizes the potential L14 of the anode electrode 102 at 1 volt relative to the hydrogen standard.

[0053] On the other hand, in the second mode, when inert gas is not supplied to the cathode electrode 104 of each unit cell 100a (see FIG. 2), the potential of the cathode electrode 104 becomes 0 volts as described above. In this case, when the second mode is started, the potential L16 of the anode electrode 102 begins to decrease due to hydrogen leaking from the cathode electrode 104 to the anode electrode 102 through the solid polymer electrolyte membrane 101, and decreases to 0 volts, which is the same potential as the cathode electrode 104.

[0054] In this way, the gas control unit 408 starts supplying inert gas from the inert gas supply unit 50 in synchronization with the start of the second mode. This allows the potential of the cathode electrode 104 to be increased to 1 volt or more relative to the hydrogen standard. Therefore, even when the second mode is started, the potential L14 of the anode electrode 102 is controlled to be equal to or higher than the elution potential of iridium. This makes it possible to suppress the oxidation-reduction reaction of iridium oxide, which is the metal catalyst of the anode electrode 102, and thus suppress the elution of iridium.

[0055] (Third embodiment) The water electrolysis apparatus 10c according to the second embodiment differs from the first embodiment in that, in the second mode, the potential of the anode electrode 102 is controlled to be equal to or higher than the elution potential of iridium by infiltrating water into the cathode electrode 104. The differences from the water electrolysis apparatus 10a according to the first embodiment are described below.

[0056] Figure 14 is a block diagram showing the configuration of a water electrolysis apparatus 10c according to the third embodiment. As shown in Figure 14, the water electrolysis apparatus 10c according to the third embodiment further includes a water supply unit 60. The water supply unit 60 includes a second circulation pump 63 and a second water tank 64. The second water tank 64 is provided vertically above the water electrolysis cell 20a.

[0057] Figure 15 is a diagram showing an example of the configuration of a single cell 100b according to the third embodiment. As shown in Figure 15, a cathode current collector 108 is disposed on a first surface of a cathode electrode 104, and a water flow path 110 is formed on a second surface opposite the first surface. This cathode current collector 108 is made of a porous material such as carbon or metal. Water is supplied from a supply port G8 of the water flow path 110 and discharged from a discharge port G10.

[0058] 14, the supply section G8 of each unit cell 100b and the second water tank 64 are connected via a second water inlet manifold 61. Meanwhile, the discharge section G10 of each unit cell 100b and the second circulation pump 63 are connected via a second water outlet manifold 62. The water electrolysis cell 20b is formed by stacking the unit cells 100b.

[0059] 16 is a block diagram showing the configuration of the control unit 40 according to the third embodiment. As shown in this FIG. 16, the control unit 40 according to this embodiment further includes a water control unit 410.

[0060] 17 is a diagram showing an example of control by the control unit 40 according to the third embodiment. The vertical axis represents potential relative to a hydrogen reference, and the horizontal axis represents time. As shown in FIG. 16, the control unit 40 performs control in the first mode for time T14, and then performs control in the second mode for time T16. In the first mode, some of the water in the anode electrode 102 moves to the cathode electrode 104 side through the solid polymer electrolyte membrane 100.

[0061] In the first mode, the water control unit 410 drives the second circulation pump 63 to suck water through the second water outlet manifold 62. As a result, water in the second water tank 64 is supplied to the water flow path 110 through the second water inlet manifold 61. Also, in the first mode, the water flow path 110 is subjected to suction by the second circulation pump 63, and as a result, the pressure therein is lower than that inside the cathode electrode 104. Therefore, the water that has moved to the cathode electrode 104 side moves to the water flow path 110 via the cathode current collector 108, because the cathode current collector 108 is porous. This enables hydrogen-gas-liquid separation processing, and the size of the hydrogen-gas-liquid separator 28 can be reduced.

[0062] On the other hand, in the second mode, the water control unit 410 stops the second circulation pump 63. As a result, the water in the second water tank 64 becomes positive pressure due to gravity, and the water in the water flow path 110 moves to the cathode electrode 104 via the cathode current collector 108, discharging hydrogen to the outside of the cathode electrode. As a result, the potential L18 of the cathode electrode 104 begins to rise and stabilizes at a potential of about 1 volt. On the other hand, the potential L20 of the anode electrode 102 begins to decrease when the second mode is started, and stops decreasing when it becomes the same potential as the cathode electrode 104. The potential L16 of the anode electrode 102 is an example when water is not purged from the cathode electrode 104.

[0063] In the second mode, a DC potential may be applied from the DC power supply 30a. For example, if the potential increase of the cathode electrode 104 due to water purging does not reach 1 volt, a potential difference of 1 volt may be applied from the DC power supply 30a to the cathode electrode 104. In this case, the connection control unit 404 may apply a second potential between the anode current collector 106 and the cathode current collector 108 of the single cell 100a by turning on the switch T10 and turning off the switches T12 and T14. For example, if the potential increase of the cathode electrode 104 due to the inert gas is 0.8 volts, the DC power supply 30a applies 0.2 volts to the cathode electrode 104. This stabilizes the potential L14 of the anode electrode 102 at 1 volt relative to the hydrogen standard.

[0064] In this way, the water control unit 410 starts supplying water at positive pressure from the second water tank 64 in synchronization with the start of the second mode. As a result, water in the water flow path 110 moves to the cathode electrode 104 via the cathode current collector 108, hydrogen is discharged to the outside of the cathode electrode, and the potential L18 of the cathode electrode 104 stabilizes at about 1 volt. Therefore, even when the second mode starts, the potential L20 of the anode electrode 102 is controlled to be equal to or higher than the elution potential of iridium. This makes it possible to suppress the oxidation-reduction reaction of iridium oxide, which is the metal catalyst of the anode electrode 102, and thus suppress the elution of iridium.

[0065] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims. [Explanation of symbols]

[0066] 10a, 10b, 10c: water electrolysis device, 20a, 20b: water electrolysis cell, 30: power supply unit, 40: control unit, 50: inert gas supply unit, 60: water supply unit, 100: solid polymer electrolyte membrane, 102: anode electrode, 104: cathode electrode, 106: anode current collector, 108: cathode current collector, 110: water flow path.

Claims

1. a water electrolysis cell having an anode electrode on one side and a cathode electrode on the other side, which uses a solid polymer electrolyte membrane to electrolyze water supplied to the anode electrode to generate hydrogen and oxygen; a power supply unit capable of changing the potential of the anode electrode; a storage unit that stores numerical examples showing a relationship between pH (which is a hydrogen ion concentration) of the anode electrode and a predetermined metal catalyst dissolution potential at the anode electrode at the pH based on thermodynamic stability; In a first mode, the power supply unit is controlled so that the potential of the anode electrode is equal to or higher than a first potential; a control unit that controls, based on the numerical example, in a second mode, a state of the water electrolysis cell so that the potential of the anode electrode is lower than the first potential and is equal to or higher than the dissolution potential of the predetermined metal catalyst at the anode electrode at the pH; A water electrolysis device comprising:

2. the control unit controls the power supply unit in the second mode, 2. The water electrolysis apparatus according to claim 1, wherein the potential of the anode electrode is set to be equal to or higher than the dissolution potential relative to a hydrogen reference.

3. the predetermined metal catalyst is iridium oxide; the control unit controls the power supply unit in the second mode, 2. The water electrolysis apparatus according to claim 1, wherein the potential of the anode electrode is set to 1 volt or more relative to a hydrogen reference.

4. the predetermined metal catalyst is iridium oxide; the control unit controls the power supply unit in the second mode, 2. The water electrolysis apparatus according to claim 1, wherein the potential of the anode electrode is set to 1 volt or more relative to the potential of the cathode electrode.

5. 5 . The water electrolysis apparatus according to claim 1 , wherein the control unit controls an inert gas supply unit that supplies an inert gas to the cathode electrode, and causes the inert gas to be supplied to the cathode electrode in the second mode.

6. a water electrolysis cell having an anode electrode on one side and a cathode electrode on the other side, which uses a solid polymer electrolyte membrane to electrolyze water supplied to the anode electrode to generate hydrogen and oxygen; a power supply unit capable of changing the potential of the anode electrode; In a first mode, the power supply unit is controlled so that the potential of the anode electrode is equal to or higher than a first potential; a control unit that, in a second mode, controls a state of the water electrolysis cell so that the potential of the anode electrode is lower than the first potential and is equal to or higher than a predetermined metal catalyst elution potential at the anode electrode; Equipped with a cathode current collector that is a porous body is disposed on a first surface of the cathode electrode, and a water flow path is formed on a second surface that faces the first surface; the control unit controls a water supply device that supplies water to the water flow path; In the first mode during hydrogen generation, the pressure of the water in the water flow path is set to be more negative than the pressure of the hydrogen in the cathode electrode, and the water that has moved to the cathode electrode side is moved to the water flow path via the cathode current collector, a water electrolysis device in which, in the second mode, the pressure of the water in the water flow path is set to be more positive than the pressure of the hydrogen in the cathode electrode, and the water in the water flow path is moved to the cathode electrode via the cathode current collector.

7. a storage unit that stores numerical examples showing a relationship between a pH (pH) that is a hydrogen ion concentration of the anode electrode and an elution potential of a predetermined metal catalyst at the anode electrode at the pH based on thermodynamic stability; 7. The water electrolysis apparatus according to claim 6, wherein, in the second mode, the control unit controls the state of the water electrolysis cell based on the numerical example so that the potential of the anode electrode is lower than the first potential and is equal to or higher than the elution potential of the predetermined metal catalyst at the anode electrode at the pH.

8. 8. The water electrolysis apparatus according to claim 7, wherein the predetermined metal catalyst is iridium oxide.

9. A method for controlling a water electrolysis cell that generates hydrogen and oxygen by electrolyzing water supplied to an anode electrode, using a solid polymer electrolyte membrane having an anode electrode on one side and a cathode electrode on the other side, and a numerical example showing, based on thermodynamic stability, a relationship between pH (which is a hydrogen ion concentration) of the anode electrode and a dissolution potential of a predetermined metal catalyst in the anode electrode at the pH, the method comprising: In the first mode, the power supply unit is controlled so that the potential of the anode electrode is equal to or higher than a first potential; and controlling, based on the numerical example, a state of the water electrolysis cell in a second mode so that the potential of the anode electrode is lower than the first potential and is equal to or higher than the dissolution potential of the predetermined metal catalyst at the anode electrode at the pH.

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