Water electrolysis device
By controlling voltage and current density during startup and shutdown, and using a valve to manage hydrogen pressure, the water electrolysis apparatus reduces hydrogen cross-leakage into the oxygen side, enhancing operational efficiency and reducing device load.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- TOYOTA JIDOSHA KK
- Filing Date
- 2022-12-20
- Publication Date
- 2026-07-07
AI Technical Summary
Existing water electrolysis devices experience increased hydrogen cross-leakage into the oxygen side path during startup and shutdown due to low current density, which is not effectively addressed by prior methods.
A water electrolysis apparatus that controls the applied voltage and current density to minimize cross-leakage by increasing the average rate of change in current density during startup and shutdown, particularly in regions where current density is less than or equal to half of the steady-state operation, and employs a valve to reduce hydrogen pressure in the hydrogen-side path.
The solution effectively suppresses hydrogen mixing into the oxygen-side pathway, reducing cross-leakage and minimizing the load on the device by ensuring efficient warm-up and shutdown processes.
Smart Images
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Abstract
Description
Technical Field
[0001] The present disclosure relates to a water electrolysis device.
Background Art
[0002] During startup and shutdown of a water electrolysis device, the hydrogen concentration in the oxygen gas to be exhausted may increase. In Patent Document 1, in the cathode depressurization process after the operation of the water electrolysis device is stopped, in order to suppress the retention of high-pressure hydrogen leaked to the anode side, a low voltage is applied from when the hydrogen supply from the cathode is stopped until the cathode pressure becomes the same as the anode pressure (or until a predetermined time has elapsed) so that hydrogen is not generated. This is disclosed.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In the technology of Patent Document 1, since an electrolysis reaction is performed at a low current with a low voltage applied, the ratio of cross leakage (mixing of hydrogen into the oxygen electrode side of the water electrolysis cell) increases.
[0005] In view of the prior art, an object of the present disclosure is to provide a water electrolysis device capable of suppressing the mixing of hydrogen into the oxygen side path (water supply side path).
Means for Solving the Problems
[0006] As a result of intensive studies, the inventor has obtained the knowledge that the ratio of cross leakage increases particularly when the current density is low during startup and shutdown of the water electrolysis device, and has solved the problem by the following specific means.
[0007] The present invention discloses a water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell and applying a voltage, comprising a water electrolysis stack in which water electrolysis cells are stacked, a water supply path for supplying water to the water electrolysis stack, a hydrogen path for recovering hydrogen generated from the water electrolysis stack, a power supply for applying a voltage to the water electrolysis stack, and a controller for controlling the applied voltage of the power supply, wherein the controller controls the voltage of the power supply such that, at startup and shutdown of the apparatus, the average rate of change of current density is greater in the region where the current density is less than or equal to half the current density during steady-state operation of the apparatus than in the region where the current density is greater than half the current density during steady-state operation.
[0008] The present invention relates to a water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell and applying voltage, comprising: a water electrolysis stack in which water electrolysis cells are stacked; a water supply path for supplying water to the water electrolysis stack; a hydrogen path for recovering hydrogen produced from the water electrolysis stack; a power supply for applying voltage to the water electrolysis stack; and a controller for controlling the applied voltage of the power supply, wherein the controller has a current density of 0.4 A / cm² at the start and stop of the apparatus. 2 The average rate of change in current density in the following region is when the current density is 0.4 A / cm². 2 Disclosed is a water electrolysis apparatus that controls the power supply to increase the average rate of change of current density in the region up to the current density during steady-state operation of the apparatus.
[0009] The present invention relates to a water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell and applying voltage, comprising a water electrolysis stack in which water electrolysis cells are stacked, a water supply path for supplying water to the water electrolysis stack, a hydrogen path for recovering hydrogen produced from the water electrolysis stack, a power supply for applying voltage to the water electrolysis stack, and a controller for controlling the applied voltage of the power supply, wherein the controller ensures that the current density is 0.4 A / cm² within 5 seconds when the apparatus is started up. 2 It reaches a certain point, and when the device stops, the current density is 0.4 A / cm². 2 Disclosed is a water electrolysis device that controls the power supply so that it shuts down within 5 seconds of reaching a certain temperature.
[0010] The above device has a valve that reduces the hydrogen pressure in the hydrogen-side path, and the controller further reduces the current density to 0.4 A / cm² before or after the current density reduction begins when the device is stopped. 2 The system may be configured to activate a valve before reaching a certain point to reduce the hydrogen pressure in the hydrogen-side path. [Effects of the Invention]
[0011] According to this disclosure, it is possible to suppress the mixing of hydrogen into the oxygen-side pathway (water supply-side pathway). [Brief explanation of the drawing]
[0012] [Figure 1] Figure 1 is a conceptual diagram illustrating the configuration of the water electrolysis system 10. [Figure 2] Figure 2 is a cross-sectional view illustrating the layer structure of the water electrolysis cell 11. [Figure 3] Figure 3 is a conceptual diagram illustrating the configuration of the controller 30. [Figure 4] Figure 4 illustrates the control of current density according to Embodiment 1. [Figure 5] Figure 5 illustrates the control of current density according to embodiment 2. [Figure 6] Figure 6 illustrates the control of current density according to embodiment 3. [Modes for carrying out the invention]
[0013] 1. Configuration of the water electrolysis device Figure 1 conceptually represents a water electrolysis apparatus 10 in one configuration. The basic principles and concepts regarding the generation of hydrogen and oxygen by water electrolysis performed in the water electrolysis apparatus 10 can be based on known standards. In this embodiment, the water electrolysis device 10 has a water electrolysis stack 20 in which a plurality of water electrolysis cells 11 are stacked and sandwiched at both ends by end plates, and a water supply side path (oxygen side path) on one side of the water electrolysis stack 20 and a hydrogen side path on the other side. In the water electrolysis device 10, water is supplied to the water electrolysis cells 11 in the water electrolysis stack 20 from the water supply side path and energized by the power supply 29 to decompose the water into hydrogen and oxygen. The obtained hydrogen is discharged into the hydrogen side path, recovered, and stored.
[0014] In the water supply path (oxygen path), tap water is purified by passing it through an ion exchanger or the like and stored in a gas-liquid separator 21. This water is then supplied to the water electrolysis stack 20 via a water pump 22 through a cooler 23 and an ion exchanger 24. The oxygen and water that exit the water electrolysis stack 20 are returned to the gas-liquid separator 21, where the gas and liquid are separated. The gas (oxygen) is discharged, and the liquid (water) is reused for water electrolysis by the water pump 22. These components are connected by piping, and configured to allow water and oxygen to flow through the necessary paths.
[0015] In the hydrogen-side path, hydrogen and associated water from the water electrolysis stack 20 are collected in the gas-liquid separator 25, where the gas and liquid are separated. The gas (hydrogen) is sent to the hydrogen tank 26 via a dehumidifier for storage. Meanwhile, the water (associated water) separated in the gas-liquid separator 25 is returned to the gas-liquid separator 21 in the water supply path via the ion exchanger 27. These components are also connected by piping, allowing water and hydrogen to flow through the necessary paths. Furthermore, this configuration includes a flow path connected to the gas-liquid separator 25, which guides hydrogen to a predetermined location by opening and closing a valve 28. By flowing hydrogen through this flow path, the hydrogen pressure in the hydrogen-side path can be reduced. The valve 28 and this flow path will be described later.
[0016] A power supply 29 is connected to the two electrodes of the water electrolysis stack 20 via a power supply line. A voltage is applied from this power supply 29 to the water electrolysis stack 20, causing water electrolysis to occur in the water electrolysis cell 11. In this embodiment, the power supply 29 and the controller 30 are electrically connected, allowing the controller 30 to control the voltage applied by the power supply 29. The power supply 29 is a well-known, standard power supply used for water electrolysis.
[0017] 1.1. Water electrolysis stack As described above, the water electrolysis stack 20 is configured by stacking multiple water electrolysis cells 11 and sandwiching them between end plates located at each end.
[0018] Figure 2 shows a cross-section of the area where water electrolysis takes place in a single water electrolysis cell 11. As can be seen from Figure 2, the water electrolysis cell 11 has a laminated structure consisting of multiple layers. The layer configuration is as known and is not particularly limited, but as shown in Figure 2, in the water electrolysis cell 11, a hydrogen electrode catalyst layer 13, a hydrogen electrode diffusion layer 15, and a hydrogen electrode separator 17 are laminated on one side of the electrolyte membrane 12, and an oxygen electrode catalyst layer 14, an oxygen electrode diffusion layer 16, and an oxygen electrode separator 18 are laminated on the other side of the electrolyte membrane 12. The hydrogen electrode separator 17 has a wave-like shape in its cross-section, forming a groove-shaped hydrogen electrode channel 17a between it and the hydrogen electrode diffusion layer 15. Hydrogen and associated water flow through this hydrogen electrode channel 17a and are discharged to the hydrogen side path. On the other hand, the oxygen electrode separator 18 also has a wave-like shape in its cross-section, forming a groove-shaped oxygen electrode channel 18a between it and the oxygen electrode diffusion layer 16. Water is supplied from the water supply side path to the oxygen electrode channel 18a, and oxygen and the remaining water are discharged from the oxygen electrode channel 18a to the water supply side path.
[0019] 1.2. Controller The controller 30 is a controller that controls the water electrolysis apparatus 10 in this embodiment. More specifically, in this embodiment, it is a controller that controls at least the applied voltage from the power supply 29 and the opening and closing of the valve 28. However, it does not have to be a controller solely for that purpose and may have other functions for controlling the water electrolysis apparatus 10. The configuration of the controller 30 is not particularly limited, but it can typically be configured as a computer. Figure 3 conceptually shows an example of the configuration of a computer 30 as the controller 30.
[0020] The computer 30 includes a CPU (Central Processing Unit) 31 which is a processor, RAM (Random Access Memory) 32 which functions as a work area, ROM (Read-Only Memory) 33 as a storage medium, a receiving unit 34 which is an interface for receiving information into the computer 30 whether wired or wireless, and an output unit 35 which is an interface for sending information from the computer 30 to the outside whether wired or wireless. A power supply 29 is connected to the receiving unit 34 and the output unit 35 in a communicative manner, and the applied voltage by the power supply 29 can be controlled by transmitting and receiving information via signals. On the other hand, a valve 28 is connected to the output unit 35 in a communicative manner, and the opening and closing of the valve 28 can be controlled.
[0021] Computer 30 stores computer programs that define each control process performed by the water electrolysis apparatus 10 in this embodiment as specific commands and execute these commands. In computer 30, the CPU 31, RAM 32, and ROM 33, which are hardware resources, work together with the computer programs. Specifically, the CPU 31 performs the function by executing the computer program recorded in ROM 33 in RAM 32, which functions as a work area, based on the applied voltage information of the power supply 29 acquired via the receiving unit 34. The information acquired or generated by the CPU 31 is stored in RAM 32. Then, based on the obtained results, commands are sent to the power supply 29 and valve 28 via the output unit 35 as needed. The specific details of the control performed by the water electrolysis device 10 will be explained next.
[0022] 2. Control by a controller (applied voltage control) In a water electrolysis device, hydrogen is discharged into the hydrogen-side path and oxygen into the oxygen-side path, with the water electrolysis cell in between. However, leakage (cross-leakage) can occur, where some hydrogen enters the oxygen-side path. It is desirable to minimize such leaked hydrogen, and it is desirable to reduce it as much as possible. In response to this, the inventors have conducted thorough research and have found that when the water electrolysis device is started up, a voltage is applied to the water electrolysis stack by the power supply, and the current density during steady-state operation (A / cm²) is reduced.2 ) until reaching it, and when the water electrolysis device is stopped, it was found that the cross-leakage ratio increases between the start of reducing the voltage applied to the water electrolysis stack by the power supply and the completion of the stop. As a result of further investigation, it was found that the problem of cross-leakage occurs in the range of low current density.
[0023] Therefore, in the water electrolysis device 10 of this embodiment, when the water electrolysis device 10 is started and stopped, the controller 30 controls the applied voltage of the power supply 29 so as to pass through the range of the low current density in as short a time as possible. As a result, the range of current density where cross-leakage is likely to occur can be shortened, so it is possible to reduce cross-leakage.
[0024] 2.1. Embodiment 1 FIG. 4 shows a diagram for explaining the control of the applied voltage according to Embodiment 1. FIG. 4 represents time on the horizontal axis and current density on the vertical axis, and is a diagram showing the change in current density from startup to shutdown. In the control of the applied voltage according to Embodiment 1, when the water electrolysis device 10 is started and stopped, in the region where the current density is less than or equal to half of the current density (M) during the steady operation of the water electrolysis device 10 (0 [A / (cm 2 ·sec)] or more and M / 2 or less), the controller 30 controls the voltage of the power supply 29 so that the average change rate of the current density is greater than that in the region where the current density is greater than half of the current density (M) during the steady operation (greater than M / 2 and less than or equal to M).
[0025] Here, the current density during "steady operation" may be the target current density when performing water electrolysis of hydrogen and oxygen by the water electrolysis device 10 and the range of the current density that is allowed as a steady state with respect to this. Therefore, the specific current density during steady operation is not particularly limited, but as an example, the current density during steady operation can be set as a target value within the range of 2.0 [A / cm 2 to 3.0 [A / cm 2 .
[0026] In addition, the average change rate of the current density can be expressed by the amount of change in the current density per unit time, and its unit is [A / (cm2 (in seconds). The average rate of change is the slope in Figure 4, and can be calculated as follows, using Figure 4 as an example. Note that the average rate of change of current density is taken as the absolute value. Here, T0 is the start time, T1 is the time when the current density becomes M / 2 at startup, T2 is the time from startup to steady operation, T3 is the time just before the start of shutdown, T4 is the time when the current density becomes M / 2 at shutdown, and T5 is the shutdown completion time. • The average rate of change of current density in the region where the current density is less than half of that during startup and steady-state operation: R1 = (M / 2) / (T1 - T0) • The average rate of change of current density in the region where the current density is greater than half of the current density during startup and steady-state operation: R2 = (M / 2) / (T2 - T1) • The average rate of change of current density in the region where the current density is greater than half of the current density during steady-state operation when the system is stopped: R3 = (M / 2) / (T4 - T3) • The average rate of change of current density in the region where the current density is less than half of that during steady-state operation when the system is stopped: R4 = (M / 2) / (T5 - T4)
[0027] In other words, R1 > R2 and R4 > R3. By controlling the applied voltage in this way, the low current density region, which is prone to cross-leakage during startup and shutdown, can be shortened, thereby suppressing the occurrence of cross-leakage.
[0028] The specific magnitude of the average rate of change of current density in such a low current density region (in this embodiment, the region of M / 2 or less) is not particularly limited, but 20 [A / (cm 2 ·sec)] or more than 500[A / (cm 2 One possible value is 40 [A / (cm²)). The higher this value, the shorter the low current density region can be. 2 Preferably 60[A / (cm²) (seconds) or more, more preferably 60[A / (cm²)]. 2The value is (i) seconds or more. On the other hand, there is no particular upper limit, but there is a time delay between the instruction by the controller 30 and the actual voltage, and the delay becomes larger the larger the average rate of change of the current density, so a temporary discrepancy is noticeable. Therefore, it can be set within a range where the discrepancy is not mistakenly judged as an error (e.g., a short circuit).
[0029] The magnitude of the average rate of change in the low current density region may be the same or different during startup and shutdown.
[0030] Furthermore, during startup, by setting R1 > R2 and increasing the time T1 to T2 to a certain extent, it becomes easier to control the change in water temperature rise that occurs with a delay in response to the increase in current density, ensure sufficient warm-up time for efficient water electrolysis, and reduce the load on the water electrolysis device 10 from the perspective of avoiding sudden changes. Similarly, during shutdown, it becomes easier to control the change in water temperature drop that occurs with a delay in response to the decrease in current density, and reduce the load on the water electrolysis device 10 from the perspective of avoiding sudden changes.
[0031] 2.2. Appearance 2 Figure 5 shows a diagram illustrating the control of the applied voltage according to Embodiment 2. Figure 5 also shows time on the horizontal axis and current density on the vertical axis, illustrating the change in current density from startup to shutdown. In the control of the applied voltage according to Embodiment 2, the current density is 0.4 A / cm² at startup and shutdown of the water electrolysis device 10. 2 The average rate of change in current density in the following region is when the current density is 0.4 A / cm². 2 The controller 30 controls the power supply 29 so that the average rate of change of current density in the region up to the current density (M) during steady-state operation of the device becomes larger. In this configuration, the average rate of change of current density can be calculated as follows, using Figure 5 as an example. Here, T 10 is the startup start time, T 11 The current density at startup is 0.4 A / cm². 2 At that time, T 12 T is the time from startup to steady-state operation.13 This is the time immediately before the stop begins, T 14 The current density is 0.4 A / cm² when stopped. 2 The time when this occurred, and T 15 This represents the time it takes for the stop to complete. ·At startup, 0.4A / cm 2 The average rate of change of current density in the region where the current density is as follows: R 11 =0.4 / (T 11 -T 10 ) ·At startup, 0.4A / cm 2 The average rate of change of current density in the region with higher current density: R 12 =(M-0.4) / (T 12 -T 11 ) ·When stopped, 0.4A / cm 2 The average rate of change of current density in the region with higher current density: R 13 =(M-0.4) / (T 14 -T 13 ) ·When stopped, 0.4A / cm 2 The average rate of change of current density in the region where the current density is as follows: R 14 =0.4 / (T 15 -T 14 )
[0032] That is, R 11 >R 12 , R 14 >R 13 This is achieved by controlling the applied voltage in this way. During startup and shutdown, the low current density region, which is prone to cross leakage, can be shortened, thereby suppressing the occurrence of cross leakage. The inventors' studies have shown that a current density of at least 0.4 A / cm² is possible. 2 The average rate of change of current density in the following region is increased, and the time (T) is increased. 10 ~T 11 It was found that shortening the ) can more significantly suppress the occurrence of cross-leakage.
[0033] This low current density region (0.4 A / cm² in this embodiment) 2The specific value of the average rate of change of current density in the following region is not particularly limited, but is 20 [A / (cm 2 ·sec)] or more than 500[A / (cm 2 One possible value is 40 [A / (cm²)). The higher this value, the shorter the low current density region can be. 2 Preferably 90[A / (cm²) (seconds) or more, and more preferably 90[A / (cm²) 2 The value is (i) seconds or more. On the other hand, there is no particular upper limit, but there is a time delay between the instruction by the controller 30 and the actual voltage, and the delay becomes larger the larger the average rate of change of the current density, so a temporary discrepancy is noticeable. Therefore, it can be set within a range where the discrepancy is not mistakenly judged as an error (e.g., a short circuit).
[0034] The average rate of change in the low current density region may be the same or different during startup and shutdown.
[0035] Furthermore, the current density at startup is 0.4 A / cm². 2 Below is the average rate of change of current density for current densities greater than or equal to M, where the current density is 0.4 A / cm². 2 The following is set to be greater than the average rate of change of current density T 11 ~T 12 By increasing the warm-up time to a certain extent, it becomes easier to control the temperature rise that occurs with a delay in response to the increase in current density, to ensure sufficient warm-up time for efficient water electrolysis, and to reduce the load on the water electrolysis device 10 from the perspective of avoiding sudden changes. Similarly, when the device is stopped, it becomes easier to control the temperature rise that occurs with a delay in response to the increase in current density, and to reduce the load on the water electrolysis device 10 from the perspective of avoiding sudden changes.
[0036] 2.3. Embodiment 3 Figure 6 shows a diagram illustrating the control of the applied voltage according to Embodiment 3. Figure 6 also shows time on the horizontal axis and current density on the vertical axis, illustrating the change in current density from startup to shutdown. In the applied voltage control according to Embodiment 3, the current density of the water electrolysis device 10 reaches 0.4 A / cm² within 5 seconds of startup. 2 When the water electrolysis device 10 stops, the current density reaches 0.4 A / cm². 2 The controller 30 controls the power supply 29 so that it stops within 5 seconds of reaching the specified value.
[0037] In this configuration, the current density is 0 A / cm² during startup and shutdown. 2 More than 0.4A / cm 2 The following range should be passed through within 5 seconds. This shortens the low current density region, which is prone to cross-leakage during startup and shutdown, thereby suppressing the occurrence of cross-leakage. The inventors' studies have shown that shortening the region where the current density is at least 0.4 A / cm² or less can more significantly suppress the occurrence of cross-leakage.
[0038] This low current density region (0.4 A / cm² in this embodiment) 2 The average rate of change of current density in the following region is not particularly limited, but 20 [A / (cm 2 ·sec)] or more than 500[A / (cm 2 One possible value is 40 [A / (cm²)). The higher this value, the shorter the low current density region can be. 2 Preferably 90[A / (cm²) (seconds) or more, and more preferably 90[A / (cm²) 2 The value is (i) seconds or more. On the other hand, there is no particular upper limit, but there is a time delay between the instruction by the controller 30 and the actual voltage, and the delay becomes larger the larger the average rate of change of the current density, so a temporary discrepancy is noticeable. Therefore, it can be set within a range where the discrepancy is not judged as an error (e.g., a short circuit).
[0039] The time spent passing through the low current density region may be the same or different during startup and shutdown.
[0040] In this configuration, the current density is 0.4 A / cm² during startup and shutdown. 2 The rate of change or time of change in the current density over a wider range is not particularly limited, and the rate of change in the current density may be maintained or changed. However, the current density is 0.4 A / cm². 2 In a larger range, the current density is 0.4 A / cm². 2 By reducing the rate of change of current density below the following range, it becomes easier to control the temperature rise that occurs with a delay in response to the increase in current density, to ensure sufficient warm-up time for efficient water electrolysis, and to reduce the load on the water electrolysis device 10 from the perspective of avoiding sudden changes. Similarly, when the device is stopped, it becomes easier to control the temperature rise that occurs with a delay in response to the increase in current density, and to reduce the load on the water electrolysis device 10 from the perspective of avoiding sudden changes.
[0041] 3. Control by a controller (valve control) When the system is stopped, although not always, the voltage may not drop even if the voltage applied by the power supply 29 is reduced. After diligent investigation, the inventors found that the reason the voltage does not drop when the system is stopped is because hydrogen remains in the water electrolysis stack 20. Therefore, in this embodiment, the controller 30 operates the valve 28 to lower the hydrogen pressure in the hydrogen-side path. This allows for a smooth decrease in voltage during shutdown.
[0042] There is no particular limit to the timing for operating valve 28 to reduce the hydrogen pressure, but it is recommended during steady-state operation before stopping, or after stopping and starting to reduce the current density when the current density reaches 0.4 A / cm². 2 It is preferable that the valve 28 is operated and the hydrogen pressure is reduced before reaching a certain point. More preferably, this occurs during steady-state operation before stopping.
[0043] The type of valve 28 should be such that it can reduce the hydrogen pressure in the hydrogen-side path and be operated by the controller 30. For example, a solenoid valve or a control valve can be used as valve 28. Furthermore, the hydrogen discharged from valve 28 may be diluted and then released, recovered in a tank or the like, or reacted with oxygen to convert it into water and heat for reuse or disposal. [Explanation of Symbols]
[0044] 10...Water electrolysis unit, 11...Water electrolysis cell, 20...Water electrolysis stack, 21...Gas-liquid separator, 22...Pump, 23...Cooler, 24...Ion exchanger, 25...Gas-liquid separator, 26...Hydrogen tank, 27...Ion exchanger, 28...Valve, 29...Power supply, 30...Controller
Claims
1. A water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell having an electrolyte membrane, a hydrogen electrode catalyst layer, a hydrogen electrode diffusion layer and a hydrogen electrode separator laminated on one side of the electrolyte membrane, and an oxygen electrode catalyst layer, an oxygen electrode diffusion layer and an oxygen electrode separator laminated on the other side of the electrolyte membrane, and applying a voltage, A water electrolysis stack in which the aforementioned water electrolysis cells are stacked, A water supply path for supplying water to the water electrolysis stack, A hydrogen side path for recovering hydrogen generated from the aforementioned water electrolysis stack, A power supply that applies the voltage to the water electrolysis stack, The system includes a controller that controls the applied voltage of the power supply, The controller is, During startup and shutdown of the device, the voltage of the power supply is controlled such that in regions where the current density is less than or equal to half of the current density during steady-state operation of the device, the average rate of change of the current density is greater than in regions where the current density is greater than half of the current density during steady-state operation. Water electrolysis equipment.
2. A water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell having an electrolyte membrane, a hydrogen electrode catalyst layer, a hydrogen electrode diffusion layer and a hydrogen electrode separator laminated on one side of the electrolyte membrane, and an oxygen electrode catalyst layer, an oxygen electrode diffusion layer and an oxygen electrode separator laminated on the other side of the electrolyte membrane, and applying a voltage, A water electrolysis stack in which the aforementioned water electrolysis cells are stacked, A water supply path for supplying water to the water electrolysis stack, A hydrogen side path for recovering hydrogen generated from the aforementioned water electrolysis stack, A power supply that applies the voltage to the water electrolysis stack, The system includes a controller that controls the applied voltage of the power supply, The controller is, During startup and shutdown of the aforementioned device, the current density is 0.4 A / cm². ２ The average rate of change in current density in the following region is "current density of 0.4 A / cm²". ２ The power supply is controlled so that it is greater than the average rate of change in current density in the region up to the current density during steady-state operation of the device. Water electrolysis equipment.
3. A water electrolysis apparatus for obtaining hydrogen and oxygen by supplying water to a water electrolysis cell having an electrolyte membrane, a hydrogen electrode catalyst layer, a hydrogen electrode diffusion layer and a hydrogen electrode separator laminated on one side of the electrolyte membrane, and an oxygen electrode catalyst layer, an oxygen electrode diffusion layer and an oxygen electrode separator laminated on the other side of the electrolyte membrane, and applying a voltage, A water electrolysis stack in which the aforementioned water electrolysis cells are stacked, A water supply path for supplying water to the water electrolysis stack, A hydrogen side path for recovering hydrogen generated from the aforementioned water electrolysis stack, A power supply that applies the voltage to the water electrolysis stack, The system includes a controller that controls the applied voltage of the power supply, The controller is, When the device is started up, the current density reaches 0.4 A / cm² within 5 seconds. ２ When the device is stopped, the current density reaches 0.4 A / cm². ２ The power supply is controlled so that it stops within 5 seconds of reaching a certain point. Water electrolysis equipment.
4. The device has a valve that reduces the hydrogen pressure in the hydrogen-side path. The controller further states that when the device is stopped, before or after the current density is reduced, the current density is 0.4 A / cm². ２ A water electrolysis apparatus according to any one of claims 1 to 3, wherein control is performed to reduce the hydrogen pressure in the hydrogen-side path by activating the valve before it reaches a certain point.