Water electrolysis system

Abstract

The present invention provides a water electrolysis system. The water electrolysis system (10) controls a power supply device (16) for flowing current between an anode electrode (32) and a cathode electrode (33) of a water electrolysis stack (12) based on the hydrogen concentration detected by a concentration sensor (22). The concentration sensor is located downstream of a pressure control valve (18) in a discharge line (40). Thus, the hydrogen concentration in the oxygen-containing gas can be maintained at a low concentration even when the temperature of the water electrolysis stack, the degradation rate of the electrolyte membrane, and the like change.

Description

Technical Field

[0001] The present invention relates to a water electrolysis system. Background Art

[0002] In recent years, in order to ensure that more people have access to affordable, reliable, sustainable, and advanced energy, research and development of systems including water electrolysis stacks that contribute to improving energy utilization efficiency has been ongoing.

[0003] The water electrolysis stack electrolyzes water to generate hydrogen and oxygen. For example, Japanese Patent Application Laid-Open No. 2022-29892 discloses a water electrolysis system having a water electrolysis stack.

[0004] Japanese Patent Application Publication No. 2022-29892 discloses a water electrolysis system comprising a water electrolysis device and an oxygen emission restriction unit. The water electrolysis device comprises an anode and a cathode separated by an ion exchange membrane. The oxygen emission restriction unit restricts the emission of oxygen generated at the anode, thereby increasing the pressure of the oxygen generated at the anode to a higher pressure than the hydrogen generated at the cathode. This prevents hydrogen from passing from the cathode to the anode and permeating the ion exchange membrane. Consequently, the hydrogen concentration in the oxygen-containing gas containing the oxygen generated at the anode is reduced. Summary of the Invention

[0005] However, since hydrogen is harmful, it is desired to further reduce the amount of hydrogen mixed in the oxygen-containing gas.

[0006] The purpose of the present invention is to solve the above technical problems.

[0007] The present invention is a water electrolysis system comprising a water electrolysis stack having: an electrolyte membrane; and an anode electrode and a cathode electrode clamping the electrolyte membrane, the water electrolysis system comprising a power supply device, a pressure control valve, a concentration sensor and a control device, wherein the power supply device causes current to flow between the anode electrode and the cathode electrode; the pressure control valve narrows a discharge pipe for flowing an oxygen-containing gas containing oxygen generated by water electrolysis in the water electrolysis stack and discharged from the water electrolysis stack; the concentration sensor is arranged at a position downstream of the pressure control valve in the discharge pipe for detecting the hydrogen concentration in the oxygen-containing gas; the control device is used to control the power supply device, and the control device adjusts the current flowing between the anode electrode and the cathode electrode based on the hydrogen concentration.

[0008] According to the above aspect, the hydrogen concentration in the oxygen-containing gas can be maintained at a low concentration even when the temperature of the water electrolysis stack, the degradation progress of the electrolyte membrane, and the like change.

[0009] The above-mentioned objects, features, and advantages will be easily understood from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram showing the structure of a water electrolysis system according to an embodiment.

[0011] Figure 2 This is a schematic diagram showing the structure of a differential pressure dryer.

[0012] Figure 3 It is a flowchart showing the steps of the control process.

[0013] Figure 4 This is a timing diagram in the control process. DETAILED DESCRIPTION

[0014] Figure 1 This is a schematic diagram showing the structure of a water electrolysis system 10 according to an embodiment. Water electrolysis system 10 can also be used in enclosed spaces. It includes a water electrolysis stack 12, a gas-liquid separator 14, a power supply 16, a pressure control valve (throttle valve) 18, a dryer 20, a concentration sensor 22, a pressure sensor 24, and a control device 26.

[0015] The water electrolysis stack 12 includes a plurality of unit cells 30 for electrolyzing water. Each unit cell 30 has the same structure. Figure 1 Only one unit cell 30 is shown. Each unit cell 30 includes an electrolyte membrane 31, an anode electrode 32, and a cathode electrode 33. The electrolyte membrane 31 is a membrane that transports hydroxide ions OH. - The electrolyte membrane 31 is sandwiched between the anode electrode 32 and the cathode electrode 33.

[0016] The anode electrode 32 of each unit cell 30 communicates with the anode outlet 35 of the water electrolysis stack 12 via a first internal flow path 34 of the water electrolysis stack 12. The cathode electrode 33 of each unit cell 30 communicates with the cathode inlet 37 and cathode outlet 38 of the water electrolysis stack 12 via a second internal flow path 36 of the water electrolysis stack 12.

[0017] In each unit cell 30, an electrochemical reaction occurs based on the voltage applied to the anode electrode 32 and the cathode electrode 33. In the cathode electrode 33, part of the water is decomposed into hydrogen ions H + and hydroxide ions OH - In the cathode electrode 33, hydrogen ions H + The cathode 30 receives electrons and generates hydrogen gas. The hydrogen-containing gas containing the hydrogen gas generated in each unit cell 30 is discharged together with water from the cathode outlet portion 38. The hydrogen-containing gas contains water vapor in addition to hydrogen gas.

[0018] Hydroxide ion OH - The hydroxide ions OH are transported to the anode electrode 32 through the electrolyte membrane 31. At the anode electrode 32, the hydroxide ions OH - Electrons are released, producing oxygen and water. Oxygen-containing gas containing the oxygen generated in each unit cell 30 is discharged from the anode outlet 35. The oxygen-containing gas contains water vapor in addition to oxygen. It also contains a small amount of hydrogen that permeates the electrolyte membrane 31 from the cathode to the anode.

[0019] The gas-liquid separator 14 separates the exhaust fluid discharged from the water electrolysis stack 12 via the output-side circulation line 41 into hydrogen-containing gas and liquid water. The hydrogen-containing gas separated by the gas-liquid separator 14 is supplied from the gas-liquid separator 14 to a designated hydrogen supply destination. The liquid water separated by the gas-liquid separator 14 is supplied from the gas-liquid separator 14 to the water electrolysis stack 12 via the input-side circulation line 42.

[0020] The power supply device 16 applies a voltage to the anode electrode 32 and cathode electrode 33 of each unit cell 30, causing current to flow between the anode electrode 32 and the cathode electrode 33. The power supply device 16 is configured to adjust the current value of the current flowing between the anode electrode 32 and the cathode electrode 33. The current value is adjusted by the control device 26.

[0021] The pressure control valve 18 is a valve that narrows the discharge line 40. By narrowing the discharge line 40, the pressure control valve 18 applies pressure to the oxygen-containing gas generated by the water electrolysis stack 12. Consequently, the pressure of the oxygen-containing gas obtained on the anode side of the water electrolysis stack 12 is higher than the pressure of the hydrogen gas obtained on the cathode side of the water electrolysis stack 12. This prevents crossover of hydrogen gas from the cathode side to the anode side, permeating the electrolyte membrane 31. Consequently, the hydrogen concentration in the oxygen-containing gas can be reduced.

[0022] In other words, the pressure control valve 18 restricts the discharge of oxygen-containing gas, which contains oxygen, generated on the anode side of each unit cell 30, thereby maintaining the pressure of the oxygen-containing gas above the pressure of the hydrogen gas generated on the cathode side of each unit cell 30. The type of pressure control valve 18 is not particularly limited, as long as it can maintain the pressure of the oxygen-containing gas above the pressure of the hydrogen gas. In this embodiment, the pressure control valve 18 is a solenoid valve with adjustable opening.

[0023] The dryer 20 is a device for drying the oxygen-containing gas. The dryer 20 is provided in the discharge line 40 between the water electrolysis stack 12 and the pressure control valve 18. In this embodiment, the dryer 20 is a differential pressure dryer. Figure 2 This is a diagram showing the structure of a differential pressure dryer.

[0024] The dryer 20 includes a duct body 51 and a plurality of hollow tubes 52. The duct body 51 is a portion of the exhaust pipe 40. The duct body 51 may be formed integrally with the exhaust pipe 40 or may be interposed between the upstream portion 43 and the downstream portion 44 of the exhaust pipe 40. Figure 2 , an example is shown in which the duct main body 51 is interposed between the upstream portion 43 and the downstream portion 44 of the discharge conduit 40 .

[0025] A gas inlet portion 53 and a gas outlet portion 54 are formed on the tube wall of the catheter body 51. The gas inlet portion 53 is arranged at a position upstream of the gas outlet portion 54. The gas inlet portion 53 may also be arranged at a position upstream of the upstream end of each hollow tube 52. The downstream end of the outlet pipe 40 is connected to the gas inlet portion 53. The oxygen supply pipe 45 is connected to the gas outlet portion 54. The oxygen supply pipe 45 is a pipe for supplying wet oxygen. In this embodiment, the downstream end of the oxygen supply pipe 45 is connected to the oxygen storage tank 60 ( Figure 1 ) In addition, a check valve 61, a filter 62, and a shutoff valve 63 are provided on the oxygen supply line 45 in order from upstream to downstream.

[0026] Each hollow tube 52 is disposed within the interior space (flow path) of the conduit body 51 and is secured to the inner wall of the conduit body 51. Each hollow tube 52 is formed from a polymer material that is highly permeable to water vapor. Each hollow tube 52 utilizes a pressure difference between the inside and outside of the hollow tube 52 to discharge water vapor from the oxygen-containing gas flowing within the hollow tube 52 into the space between the hollow tube 52 and the discharge line 40.

[0027] The oxygen-containing gas discharged from the water electrolysis stack 12 to the upstream portion 43 of the discharge conduit 40 flows into the conduit body 51 of the dryer 20. A portion of the oxygen-containing gas flowing into the conduit body 51 passes through the interior space of each hollow tube 52. The remaining portion of the oxygen-containing gas flowing into the conduit body 51 flows out of the gas discharge portion 54 to the oxygen supply conduit 45.

[0028] The oxygen-containing gas passing through the interior space of each hollow tube 52 flows from the downstream end of the hollow tube 52 into the downstream portion 44 of the discharge line 40. The oxygen-containing gas flowing in the downstream portion 44 of the discharge line 40 is dry. The dry oxygen-containing gas flows from the gas inlet portion 53 connected to the downstream end of the discharge line 40 into the space between the conduit body 51 (discharge line 40) and the hollow tube 52. This space is in a humidified state, and the oxygen-containing gas flowing into this space is humidified. The humidified oxygen-containing gas flows to the oxygen supply line 45 or the downstream portion 44 of the discharge line 40.

[0029] The concentration sensor 22 is a sensor for detecting the hydrogen concentration in the oxygen-containing gas. It is located in the discharge line 40, downstream of the pressure control valve 18. The pressure of the oxygen-containing gas flowing downstream of the pressure control valve 18 is lower than the pressure of the oxygen-containing gas flowing upstream of the pressure control valve 18. Consequently, the relative humidity of the oxygen-containing gas decreases. Therefore, compared to installing the concentration sensor 22 upstream of the pressure control valve 18 in the discharge line 40, the decrease in measurement accuracy due to moisture can be suppressed. Furthermore, the concentration sensor 22 is located downstream of the dryer 20. Therefore, the decrease in measurement accuracy due to moisture can be suppressed.

[0030] The pressure sensor 24 is a sensor for detecting the pressure of the oxygen-containing gas. The pressure sensor 24 is installed in the discharge line 40 between the water electrolysis stack 12 and the pressure control valve 18. In this embodiment, the pressure sensor 24 is installed in the discharge line 40 between the water electrolysis stack 12 and the dryer 20.

[0031] The control device 26 is a computer that centrally manages the water electrolysis system 10. The control device 26 includes one or more processors and a storage medium. The storage medium may be composed of volatile memory and non-volatile memory. Examples of the processor include a CPU and an MCU. Examples of volatile memory include RAM. Examples of non-volatile memory include ROM and flash memory.

[0032] The control device 26 executes control processing when receiving a start-up instruction for the water electrolysis stack 12 , for example. Figure 3 It is a flowchart showing the steps of the control process. Figure 4 This is a timing chart for the control process. Furthermore, before the water electrolysis stack 12 is started (in a stopped state), the pressure control valve 18 is closed, and no gas is supplied downstream of the pressure control valve 18. Furthermore, before the water electrolysis stack 12 is started (in a stopped state), the shutoff valve 63 is closed, and no gas is supplied downstream of the shutoff valve 63.

[0033] In step S1, the control device 26 controls the power supply device 16 to start flowing a current of a preset initial current value between the anode electrode 32 and the cathode electrode 33 of each unit cell 30. In this case, the current value of the current flowing between the anode electrode 32 and the cathode electrode 33 gradually increases (see Figure 4 As the current increases, water electrolysis begins in the water electrolysis stack 12, and the pressure of the oxygen-containing gas generated in the water electrolysis stack 12 increases (see Figure 4 ).

[0034] The control device 26 starts measurement by the concentration sensor 22 and the pressure sensor 24. In this case, the control device 26 begins storing the hydrogen concentration in the oxygen-containing gas detected by the concentration sensor 22 and the pressure of the oxygen-containing gas detected by the pressure sensor 24, along with the detection time, in the storage medium. When the current supply between the electrodes of each unit cell 30 and the sensor measurement start, the control process shifts to step S2.

[0035] In step S2, the control device 26 determines whether to continue the operation of the water electrolysis stack 12. When the first condition or the second condition is not satisfied, the control device 26 determines that the operation of the water electrolysis stack 12 is not continued. In this case, the control process ends. On the other hand, when the first condition or the second condition is satisfied, the control device 26 determines that the operation of the water electrolysis stack 12 is continued. In this case, the control process transfers to step S3. The first condition refers to a situation where the current value does not reach the initial value even after a prescribed first period has passed after the start of power supply between the electrodes of each single cell 30. The second condition refers to a situation where the pressure of the oxygen-containing gas detected by the pressure sensor 24 does not reach the prescribed pressure threshold even after a prescribed second period has passed after the start of power supply between the electrodes of each single cell 30.

[0036] In step S3, the control device 26 obtains the current value from the power supply device 16 and compares the current value with the initial value. If the current value is less than the initial value, the control process returns to step S2. On the other hand, if the current value is greater than the initial value, the control process moves to step S4.

[0037] In step S4, the control device 26 obtains the current pressure detected by the pressure sensor 24 and compares the current pressure with a predetermined pressure threshold. If the current pressure is less than the pressure threshold, the control process returns to step S2. On the other hand, if the current pressure is greater than the pressure threshold, the control process shifts to step S5.

[0038] In step S5, the control device 26 opens the pressure control valve 18 (see Figure 4 In this case, the control device 26 adjusts the opening of the pressure control valve 18 so that the flow path is narrower than the discharge line 40. Furthermore, the control device 26 opens the shutoff valve 63. When the pressure control valve 18 and the shutoff valve 63 are opened, the control process shifts to step S6.

[0039] In step S6, the control device 26 obtains the current hydrogen concentration detected by the concentration sensor 22 and compares the current hydrogen concentration with a predetermined concentration threshold. If the current hydrogen concentration is less than the concentration threshold, the control process stops at step S6. On the other hand, if the current hydrogen concentration is greater than the concentration threshold, the control process shifts to step S7.

[0040] In step S7, the control device 26 increases the current flowing between the electrodes of each unit cell 30. In this case, the control device 26 adds a predetermined additional value VL (see Figure 4 ) is set as the target current value. After setting the target current value, the control device 26 controls the power supply device 16 so that the current of the target current value flows. When the current flowing between the electrodes of each unit cell 30 increases, the reaction rate of water electrolysis in the water electrolysis stack 12 is accelerated. Therefore, the pressure of the oxygen-containing gas generated in the water electrolysis stack 12 increases (refer to Figure 4 ). When the current of the target current value starts to flow, the control process shifts to step S8.

[0041] In step S8, the control device 26 determines whether to continue the operation of the water electrolysis stack 12. If the third condition is met, the control device 26 determines to continue the operation of the water electrolysis stack 12. In this case, the control process returns to step S6. On the other hand, if the third condition is not met, the control device 26 determines not to continue the operation of the water electrolysis stack 12. In this case, the control process transfers to step S9. The third condition is that even if the added value VL is added a predetermined number of times, the hydrogen concentration detected by the concentration sensor 22 does not fall below the concentration threshold.

[0042] In step S9, the control device 26 stops the flow of electricity between the electrodes of each cell 30 and closes the pressure control valve 18 and the shutoff valve 63. When the flow of electricity between the electrodes of each cell 30 is stopped and the pressure control valve 18 and the shutoff valve 63 are closed, the control process ends.

[0043] In this manner, the control device 26 adjusts the current flowing between the electrodes of each unit cell 30 based on the hydrogen concentration in the oxygen-containing gas exhausted from the water electrolysis stack 12. This allows the hydrogen concentration in the oxygen-containing gas to be maintained at a low level even when the temperature of the water electrolysis stack 12 or the degradation rate of the electrolyte membrane 31 changes.

[0044] In this embodiment, the control device 26 closes the pressure control valve 18 from the start of current flow until the pressure detected by the pressure sensor 24 reaches a predetermined pressure threshold. When the pressure reaches the pressure threshold, the control device 26 opens the pressure control valve 18. This allows the pressure of the oxygen-containing gas to be increased more quickly than when the pressure control valve 18 is always open, resulting in a reduction in the hydrogen concentration in the oxygen-containing gas.

[0045] In this embodiment, the control device 26 adjusts the current flowing between the electrodes of each cell 30 after opening the pressure control valve 18. This reduces the control load of the control device 26 and, as a result, improves energy efficiency.

[0046] The above-mentioned embodiment may be modified as follows.

[0047] For example, the downstream end of the oxygen supply line 45 may be open to a room instead of being connected to the oxygen storage tank 60. Furthermore, the room may be formed inside a mobile object that can move into an enclosed space. In this case, the water electrolysis system 10 is mounted on the mobile object.

[0048] In the water electrolysis system 10 of the above-described embodiment, the oxygen-containing gas passing from the water electrolysis stack 12 through the interior space of the hollow tube 52 has its moisture reduced and is supplied to the concentration sensor 22 provided in the discharge line 40. The oxygen-containing gas then returns from the downstream end of the discharge line 40 to the space outside the hollow tube 52, where it is humidified. The humidified oxygen-containing gas is then supplied to the room, replacing the oxygen storage tank 60, via the oxygen supply line 45. This prevents the measurement accuracy of the concentration sensor 22 from being degraded due to moisture, while also supplying oxygen-containing gas humidified to a state suitable for human breathing to the room. Furthermore, since the oxygen-containing gas generated by the water electrolysis stack 12 is dried and then rehumidified before being supplied to the room, the utilization efficiency of the oxygen-containing gas can be improved.

[0049] Alternatively, for example, dryer 20 may be a heat exchange dryer. In this case, dryer 20 can utilize the heat generated by water electrolysis stack 12. Alternatively, dryer 20 may be removed. In this case, the downstream end of discharge line 40 is connected to oxygen storage tank 60. A check valve 61, a filter 62, and a shutoff valve 63 are provided in discharge line 40.

[0050] Furthermore, for example, the oxygen supply line 45 may supply oxygen to a destination such as a room of a mobile object equipped with the water electrolysis system 10 .

[0051] Furthermore, for example, the control device 26 may gradually increase the current value of the current flowing between the electrodes of each unit cell 30 while the hydrogen gas concentration detected by the concentration sensor 22 exceeds a predetermined concentration threshold.

[0052] The invention and effects that can be grasped from the above description are described below.

[0053] (1) The present invention is a water electrolysis system (10) comprising a water electrolysis stack (12) having an electrolyte membrane (31) and an anode electrode (32) and a cathode electrode (33) sandwiching the electrolyte membrane. The water electrolysis system comprises a power supply device (16), a pressure control valve (18), a concentration sensor (22), and a control device (26), wherein the power supply device allows current to flow between the anode electrode and the cathode electrode; the pressure control valve narrows a discharge pipe (40) through which oxygen-containing gas generated by water electrolysis in the water electrolysis stack flows; the concentration sensor is disposed in the discharge pipe at a position downstream of the pressure control valve and is used to detect the hydrogen concentration in the oxygen-containing gas; and the control device is used to control the power supply device, and the control device adjusts the current flowing between the anode electrode and the cathode electrode based on the hydrogen concentration.

[0054] This allows the hydrogen concentration in the oxygen-containing gas to be maintained at a low level even when the temperature of the water electrolysis stack or the degradation rate of the electrolyte membrane changes. Furthermore, the concentration sensor is located downstream of the pressure control valve in the discharge line. Therefore, the pressure of the oxygen-containing gas flowing downstream of the pressure control valve is lower than that flowing upstream of the pressure control valve. As a result, the relative humidity of the oxygen-containing gas decreases. Therefore, compared to installing the concentration sensor upstream of the pressure control valve in the discharge line, the decrease in measurement accuracy due to moisture can be suppressed.

[0055] (2) In the water electrolysis system of the present invention, the control device may increase the current when the hydrogen concentration exceeds a predetermined concentration threshold. This accelerates the water electrolysis reaction rate of the water electrolysis stack, increasing the pressure of the oxygen-containing gas obtained on the anode side of the water electrolysis stack. As a result, the amount of hydrogen that passes through the electrolyte membrane from the cathode side to the anode side can be reduced, thereby lowering the hydrogen concentration in the oxygen-containing gas.

[0056] (3) In the water electrolysis system of the present invention, when the hydrogen concentration exceeds a predetermined concentration threshold, the control device may set a target current value by adding a predetermined additional value (VL) to the current current value, and control the power supply device so that the current of the target current value flows. In this manner, the current can be increased in stages each time the hydrogen concentration exceeds the concentration threshold. As a result, the hydrogen concentration in the oxygen-containing gas can be reduced in stages.

[0057] (4) In the water electrolysis system of the present invention, a pressure sensor (24) may be further provided in the discharge line between the water electrolysis stack and the pressure control valve for detecting the pressure of the oxygen-containing gas. The pressure control valve can be opened and closed by the control of the control device. The control device closes the pressure control valve from the start of the flow of the current until the pressure reaches a predetermined pressure threshold, and opens the pressure control valve when the pressure reaches the pressure threshold. In this way, the pressure of the oxygen-containing gas can be increased more quickly than when the pressure control valve is always open, and as a result, the hydrogen concentration in the oxygen-containing gas can be reduced.

[0058] (5) In the water electrolysis system of the present invention, the control device may adjust the current after the pressure control valve is opened. This can reduce the control load of the control device and, as a result, improve energy utilization efficiency.

[0059] (6) The water electrolysis system of the present invention may further include a dryer (20) disposed in the discharge line between the water electrolysis stack and the pressure control valve for drying the oxygen-containing gas. This can suppress a decrease in the measurement accuracy of the concentration sensor due to moisture.

[0060] (7) In the water electrolysis system of the present invention, the dryer may include a hollow tube (52) disposed inside the exhaust pipe, capable of discharging water vapor in the oxygen-containing gas. The hollow tube discharges the water vapor in the oxygen-containing gas flowing inside the hollow tube into the space between the hollow tube and the exhaust pipe due to the pressure difference between the inside and outside of the hollow tube. This makes it easier to suppress operating energy compared to a heat exchange dryer. As a result, energy utilization efficiency can be improved.

[0061] (8) In the water electrolysis system of the present invention, a gas inlet portion (53) and a gas outlet portion (54) may be formed on the wall of the discharge pipe in which the hollow pipe is disposed, the downstream end of the discharge pipe downstream of the pressure control valve being connected to the gas inlet portion, and an oxygen supply pipe (45) for supplying wet oxygen being connected to the gas outlet portion. Thus, dry oxygen-containing gas can be supplied to the concentration sensor while wet oxygen-containing gas can be supplied to the supply target.

[0062] In addition, the present invention is not limited to the above-mentioned disclosure, and various structures can be adopted within the scope not departing from the gist of the present invention.

Claims

1. A water electrolysis system comprising a water electrolysis stack having: an electrolyte membrane; and an anode electrode and a cathode electrode sandwiching the electrolyte membrane, It is characterized in that It includes a power supply device, a pressure control valve, a concentration sensor and a control device, wherein: The power supply device causes current to flow between the anode electrode and the cathode electrode; The pressure control valve narrows a discharge line for the flow of oxygen-containing gas discharged from the water electrolysis stack and generated by water electrolysis in the water electrolysis stack; The concentration sensor is arranged at a position downstream of the pressure control valve in the discharge pipeline, and is used to detect the hydrogen concentration in the oxygen-containing gas; The control device is used to control the power supply device, The control device increases the current flowing between the anode electrode and the cathode electrode when the hydrogen gas concentration exceeds a predetermined concentration threshold.

2. The water electrolysis system according to claim 1, characterized in that When the hydrogen gas concentration exceeds the predetermined concentration threshold, the control device sets a target current value by adding a predetermined additional value (VL) to a current current value, and controls the power supply device so that the current of the target current value flows.

3. The water electrolysis system according to claim 1, characterized in that A pressure sensor is also provided, which is arranged in the discharge pipeline between the water electrolysis stack and the pressure control valve, and is used to detect the pressure of the oxygen-containing gas. The pressure control valve can be opened and closed by the control device. The control device closes the pressure control valve from the start of the flow of the current until the pressure reaches a predetermined pressure threshold, and opens the pressure control valve when the pressure reaches the pressure threshold.

4. The water electrolysis system according to claim 3, characterized in that The control device adjusts the current after the pressure control valve is opened.

5. The water electrolysis system according to claim 1, characterized in that A dryer is further provided in the exhaust line between the water electrolysis stack and the pressure control valve for drying the oxygen-containing gas.

6. The water electrolysis system according to claim 5, characterized in that The dryer has a hollow tube, which is arranged inside the exhaust pipe and can discharge water vapor in the oxygen-containing gas. The hollow tube discharges the water vapor in the oxygen-containing gas flowing inside the hollow tube into a space between the hollow tube and the discharge line due to a pressure difference between the inside and outside of the hollow tube.

7. The water electrolysis system according to claim 6, characterized in that A gas inlet portion and a gas outlet portion are formed on a pipe wall of the exhaust pipe in which the hollow pipe is disposed. The downstream end of the discharge line, which is downstream of the pressure control valve, is connected to the gas inlet portion. An oxygen supply line for supplying wet oxygen is connected to the gas discharge portion.

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