METHOD FOR CARRYING OUT WATER ELECTROLYSIS

Abstract

Method for carrying out water electrolysis using a water electrolysis device (10), wherein hydrogen and oxygen are obtained by supplying water to water electrolysis cells (11) and applying a voltage to the water electrolysis cells (11), the water electrolysis device (10) comprising: a water electrolysis stack (20) in which the water electrolysis cells (11) are stacked; a water supply channel through which water is supplied to the water electrolysis stack (20); a hydrogen supply channel through which the hydrogen produced by the water electrolysis stack (20) is collected; an electric current source (29) that applies the voltage to the water electrolysis stack (20);and a control device (30) that controls the applied voltage of the electrical current source (29), wherein at the times of switching on and stopping the water electrolysis device (10) the control device (30) controls the voltage of the electrical current source (29) such that a mean rate of change of a current density in a range where the current density is equal to or less than half a current density at a time of continuous operation of the water electrolysis device (10) is higher than in a range where the current density is greater than half a current density at the time of continuous operation.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a water electrolysis device. 2. Description of the state of the art

[0002] When starting or stopping a water electrolysis device, the hydrogen concentration in the emitted oxygen gas sometimes increases. Japanese Patent Application No. 2010-236089 (JP 2010-236089 A) discloses that a low voltage that prevents hydrogen generation is applied until the cathode pressure reaches the same value as the anode pressure (or until a predetermined time has elapsed) after the hydrogen supply from the cathode is stopped, in order to prevent the retention of high-pressure hydrogen escaping to the anode side in a cathode pressure reduction process after the operation of the water electrolysis device is stopped. SUMMARY OF THE INVENTION

[0003] The technology described in JP 2010-236089 A applies a low voltage and conducts the electrolysis reaction at a low current. Therefore, the cross-leakage rate (the mixing of hydrogen with the oxygen electrode side of water electrolysis cells) increases.

[0004] In view of the prior art, the present invention has an object to provide a water electrolysis apparatus that can restrict the mixing of hydrogen with an oxygen-side channel (water supply-side channel).

[0005] As a result of diligent investigations, the inventor has recognized that the ratio of transverse leakage increases particularly when the current density is low at the times of turning on and stopping the water electrolyzer, and has solved the problem by the following specific means.

[0006] The present patent application discloses a water electrolysis device that performs water electrolysis in which hydrogen and oxygen are obtained by supplying water to water electrolysis cells and applying a voltage to the water electrolysis cells, the water electrolysis device comprising: a water electrolysis stack in which the water electrolysis cells are stacked; a water supply-side channel through which water is supplied to the water electrolysis stack; a hydrogen-side channel through which hydrogen generated by the water electrolysis stack is collected; an electric power source that applies the voltage to the water electrolysis stack; and a control device that controls the applied voltage of the electric power source, the control device being configured to control the applied voltage of the electric power source at the times of starting up and stopping.of stopping the water electrolysis device, controlling the voltage of the electric power source so that an average rate of change of a current density in a region where the current density is equal to or lower than half of a current density at a time of continuous operation of the water electrolysis device is higher than in a region where the current density is higher than half of the current density at the time of continuous operation.

[0007] The present patent application discloses a water electrolysis device that performs water electrolysis in which hydrogen and oxygen are obtained by supplying water to water electrolysis cells and applying a voltage to the water electrolysis cells, the water electrolysis device comprising: a water electrolysis stack in which the water electrolysis cells are stacked; a water supply-side channel through which water is supplied to the water electrolysis stack; a hydrogen-side channel through which hydrogen generated by the water electrolysis stack is collected; an electric power source that applies the voltage to the water electrolysis stack;and a control device that controls the application voltage of the electric power source, wherein at the times of turning on and stopping the water electrolysis device, the control device controls the electric power source so that an average change rate of a current density in a range where the current density is equal to or less than 0.4 A / cm; 2 is higher than in an area where the current density is higher than 0.4 A / cm 2 and is equal to or lower than a current density at the time of continuous operation of the water electrolysis device.

[0008] The present patent application discloses a water electrolysis device that performs water electrolysis in which hydrogen and oxygen are obtained by supplying water to water electrolysis cells and applying a voltage to the water electrolysis cells, the water electrolysis device comprising: a water electrolysis stack in which the water electrolysis cells are stacked; a water supply-side channel through which water is supplied to the water electrolysis stack; a hydrogen-side channel through which hydrogen generated by the water electrolysis stack is collected; an electric power source that applies the voltage to the water electrolysis stack; and a control device that controls the application voltage of the electric power source, the control device controlling the electric power source such that a current density of 0.4 A / cm 2within 5 seconds at a time of switching on the water electrolyzer and the water electrolyzer reaches a stopped state within 5 seconds after the current density reaches 0.4 A / cm 2 at a time of stopping the water electrolysis device.

[0009] The above water electrolysis device may include a valve that reduces a hydrogen pressure of the hydrogen-side channel, and at the time of stopping the water electrolysis device, the control device may further perform control to operate the valve and reduce the hydrogen pressure of the hydrogen-side channel before the current density is reduced or before the current density reaches 0.4 A / cm 2 reached after the current density begins to be reduced.

[0010] With the present invention, it is possible to restrict the mixing of hydrogen to the oxygen-side channel (water supply-side channel). BRIEF DESCRIPTION OF THE DRAWING

[0011] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which like reference numerals designate like elements and in which: Fig. 1 is a conceptual diagram for describing the configuration of a water electrolysis device 10; Fig. 2 is a sectional view for describing the layer structure of a water electrolysis cell 11; Fig. 3 is a conceptual diagram for describing the configuration of a control device 30; Fig. 4 is a diagram for describing a control of a current density according to an aspect 1; Fig. 5 is a diagram for describing a current density control according to an aspect 2; and Fig. 6 is a diagram for describing a current density control according to an aspect 3. DETAILED DESCRIPTION OF THE EMBODIMENTS 1. Configuration of the water electrolysis device

[0012] Fig. Figure 1 conceptually shows a water electrolysis device 10 according to an embodiment. Known principles and ideas can be adopted as the basic principle and idea relevant to the generation of hydrogen and oxygen by water electrolysis performed in the water electrolysis device 10. In the embodiment, the water electrolysis device 10 includes a water electrolysis stack 20 in which a plurality of water electrolysis cells 11 are stacked, and both ends of the water electrolysis cells 11 are enclosed by end plates, a water supply-side channel (oxygen-side channel) on one side of the water electrolysis stack 20, and a hydrogen-side channel on the other side.In the water electrolysis device 10, water is supplied from the water supply channel to the water electrolysis cells 11 comprising the water electrolysis stack 20. Power is supplied by an electric power source 29, so that the water is decomposed into hydrogen and oxygen. The resulting hydrogen is discharged into the hydrogen-side channel, collected, and stored.

[0013] On the water supply side channel (oxygen side channel), city water is converted into pure water, for example, by an ion exchanger. The pure water is stored in a gas-liquid separator 21 and then supplied to the water electrolysis stack 20 through a cooler 23 and an ion exchanger 24 by a water pump 22. The oxygen and water discharged from the water electrolysis stack 20 are returned to the gas-liquid separator 21 and separated into gas and liquid. The gas (oxygen) is exhausted, and the liquid (water) is reused for water electrolysis by the water pump 22. These elements are connected by pipes and designed to allow the water and oxygen to flow through the required channels.

[0014] On the hydrogen-side channel, the hydrogen and produced water discharged from the water electrolysis stack 20 are collected in the gas-liquid separator 25 and separated into gas and liquid. The gas (hydrogen) is supplied to a hydrogen tank 26 via a dehydrator and stored there. On the other hand, the water (produced water) after separation by the gas-liquid separator 25 is returned to the gas-liquid separator 21 on the water supply-side channel through the ion exchanger 27. These elements are also connected to each other by pipes and configured to allow the water and hydrogen to flow through the required channels. Furthermore, in the embodiment, there is a flow passage connected to the gas-liquid separator 25, through which the hydrogen is supplied to a predetermined location by opening and closing a valve 28.By allowing hydrogen to flow through the flow passage, the hydrogen pressure in the hydrogen-side channel can be reduced. Valve 28 and the flow passage will be described later.

[0015] The power source 29 is connected to both electrodes of the water electrolysis stack 20 via power source wires. The electric power source 29 applies a voltage to the water electrolysis stack 20, thereby generating water electrolysis by the water electrolysis cells 11. Furthermore, in the embodiment, the electric power source 29 and the control device 30 are electrically connected, and the control device 30 is configured to be able to control the application voltage of the electric power source 29. The electric power source 29 is known, and a conventional electric power source used for water electrolysis can be adopted. 1.1. Water electrolysis stack

[0016] As described above, the water electrolysis stack 20 is configured such that the water electrolysis cells 11 are stacked and enclosed by the end plates arranged at both ends of the water electrolysis cells 11, respectively.

[0017] Fig. Figure 2 shows a cross-section of a location in the water electrolysis cell 11 where water electrolysis is carried out. As in Fig. As shown in Figure 2, the water electrolysis cell 11 has a layered structure consisting of a plurality of layers. The arrangement of the layers is known and not particularly limited. As shown in Fig. 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 layered on one side of an electrolyte film 12, and an oxygen electrode catalyst layer 14, an oxygen electrode diffusion layer 16, and an oxygen electrode separator 18 are layered on the other side of the electrolyte film 12. The hydrogen electrode separator 17 has a wave shape in cross section and forms a groove-shaped flow passage 17a between the hydrogen electrode separator 17 and the hydrogen electrode diffusion layer 15. The hydrogen and the generated water flow through the hydrogen electrode flow passage 17a and are discharged into the hydrogen-side channel.The oxygen electrode separator 18 is also wave-shaped in cross section and forms a groove-shaped flow passage 18a between the oxygen electrode separator 18 and the oxygen electrode diffusion layer 16. The water is supplied from the water supply side channel into the flow passage 18a of the oxygen electrode, and the oxygen and the remaining water are discharged from the flow passage 18a of the oxygen electrode into the water supply side channel. 1.2. Control device

[0018] The control device 30 is a control device that controls the water electrolysis device 10 in the embodiment. More specifically, the controller 30 in the embodiment is a control device that controls at least the application voltage of the electric power source 29 and the opening and closing of the valve 28. However, the control device 30 does not necessarily have to be a control device that only controls the application voltage of the electric power source 29 and the opening and closing of the valve 28, but may also have other functions for controlling the water electrolysis device 10. The aspect of the control device 30 is not particularly limited and can typically be constituted by a computer. Fig. 3 conceptually shows a configuration example of a computer 30 as a control device 30.

[0019] The computer 30 includes a central processing unit (CPU) 31, which is a processor, a random access memory (RAM) 32, which functions as a work area, a read-only memory (ROM) 33, which serves as a storage medium, a receiving unit 34, which is an interface for wired or wireless input of information to the computer 30, and an output unit 35, which is an interface for wired or wireless transmission of information from the computer 30 to the outside. The electric power source 29 is communicatively connected to the receiving unit 34 and the output unit 35 and is configured to be able to control the application voltage of the electric power source 29 by transmitting and receiving information through signals. On the other hand, the valve 28 is communicatively connected to the output unit 35 and configured to be able to control the opening and closing of the valve 28.

[0020] The computer 30 stores a computer program for executing specific commands, which are processes for controlling the water electrolysis device 10 in this embodiment. In the computer 30, the CPU 31, the RAM 32, and the ROM 33 cooperate with the computer program as hardware resources. Specifically, the CPU 31 executes functions by executing the computer program recorded in the ROM 33 in the RAM 32, which functions as a work area, based on information about the application voltage of the electric power source 29 and the like acquired via the receiving unit 34. The information acquired or generated by the CPU 31 is stored in the RAM 32. Then, based on the obtained result, a command is sent to the electric power source 29 or the valve 28 through the output unit 35, if necessary.

[0021] Next, a specific content of the control by the water electrolysis device 10 will be described. 2. Control (application voltage control) by the control device

[0022] In the water electrolysis device, hydrogen is discharged through the water electrolysis cells via the hydrogen-side channel, and oxygen is discharged through the oxygen-side channel. In some cases, leakage (cross leakage) occurs, causing some hydrogen to enter the oxygen-side channel. The amount of leaked hydrogen should be small, and therefore, it is desirable to reduce the leaked hydrogen as much as possible. Therefore, as a result of diligent research, the inventor found that the ratio of cross leakage in a period after the voltage is applied to the water electrolysis stack by the electric power source and before the current density reaches a current density (A / cm 2) at the time of continuous operation, increases in the case of the time of turning on the water electrolyzer, and increases in a period after the application of voltage to the water electrolyzer stack by the electric power source begins to decrease and before the stoppage of the water electrolyzer is completed, in the case of the time of stopping the water electrolyzer. Furthermore, through further in-depth investigations, the inventor has found that the problem of cross leakage occurs particularly in a region where the current density is low.

[0023] Therefore, in the water electrolysis device 10 in this embodiment, the control device 30 controls the application voltage of the electric power source 29 so that the time of the low current density region at the time of starting and stopping the water electrolysis device 10 is as short as possible. This makes it possible to shorten the current density range in which cross leakage is likely to occur, and thus to reduce cross leakage. 2.1. Aspect 1

[0024] Fig. 4 shows a diagram for describing a control of the application voltage according to an aspect 1. Fig. Figure 4 is a graph showing a change in current density from the time of turning on to the time of stopping. The abscissa axis indicates time, and the ordinate axis indicates the current density. In the control of the applied voltage according to aspect 1, the control device 30 controls the voltage of the electric power source 29 at the times of turning on and stopping the water electrolysis device 10 such that the average change rate of the current density is in a range (0 [A / (cm 2 · second)] or higher and M / 2 or lower) in which the current density is equal to or lower than half of a current density (M) at the time of continuous operation of the water electrolyzer 10, is higher than in a region (higher than M / 2 and M or lower) in which the current density is higher than half of the current density (M) at the time of continuous operation.

[0025] The current density at the time of "continuous operation" only needs to be a target current density when water electrolysis for hydrogen and oxygen is carried out by the water electrolysis device 10, or a current density within a range that is permissible as a steady state with respect to the target current density. Accordingly, the specific current density at the time of continuous operation is not particularly limited. For example, a current density within a range of 2.0 [A / cm 2 ] to 3.0 [A / cm 2 ] can be assumed as the setpoint at the time of continuous operation.

[0026] Furthermore, the average rate of change of current density can be expressed as the amount of change of current density per unit time, and the unit of the average rate of change of current density is [A / (cm 2 second). The mean rate of change is the slope in Fig. 4 and can, as in the following description using the example of Fig. 4. The average change rate of current density is an absolute value. Here, T0 denotes a start time, T1 a time when the current density becomes M / 2 at the time of start, T2 a time when the continuous operation starts after the start time, T3 a time immediately before the start of stop, T4 a time when the current density becomes M / 2 at the time of stop, and T5 a time when the stop is completed. - The average rate of change of current density is in the range where the current density is equal to or less than half of the current density at the time of continuous operation, in the case of the time of switching on: R1 = (M / 2) / (T1-T0) - The average rate of change of current density in the range where the current density is higher than half of the current density at the time of continuous operation, in the case of the moment of switching on: R2 = (M / 2) / (T2-T1) - The average rate of change of current density is in the range where the current density is higher than half of the current density at the time of continuous operation, in the case of the time of stopping: R3 = (M / 2) / (T4-T3) - The average rate of change of current density is in the range where the current density is equal to or less than half of the current density at the time of continuous operation, in the case of the time of stopping: R4 = (M / 2) / (T5-T4)

[0027] That is, R1 > R2 and R4 > R3 are satisfied. By controlling the applied voltage at the times of turn-on and stop, it is possible to shorten the range where the current density is low and where cross leakage is prone to occur, and it is possible to prevent the occurrence of cross leakage.

[0028] The specific value of the average change rate of the current density in the region where the current density is low (in the embodiment, the region where the current density is M / 2 or lower) is not particularly limited and may be 20 [A / (cm 2 ·second)] or higher and 500 [A / (cm 2 ·second)] or lower. Since this value is higher, the range where the current density is low can be shortened. Therefore, a value of 40 [A / (cm 2 ·second)] or higher is preferable, and a value of 60 [A / (cm 2A time delay of 1 second or higher is even more preferable. On the other hand, the upper limit of the value is not particularly limited. There is a time delay between the command from the control device 30 and the actual voltage being reached. The higher the average change rate of the current density, the longer the delay and the larger the time gap. Therefore, the upper limit of the value can be set within a range such that the gap is not mistakenly detected as a fault (e.g., short circuit).

[0029] Between the time of switching on and the time of stopping, the value of the average rate of change may be the same or different in the area where the current density is low.

[0030] At the time of power-on, by setting R1 > R2, the time from T1 to T2 is set to be reasonably long. This makes it possible to easily control the change in the water temperature rise that occurs behind the increase in the current density, to efficiently perform water electrolysis by ensuring sufficient warm-up time, and to reduce the load on the water electrolyzer 10 from the perspective of avoiding a sudden change. Similarly, at the time of stopping, it is possible to easily control the change in the water temperature drop that occurs behind the drop in the current density and to reduce the load on the water electrolyzer 10 from the perspective of avoiding a sudden change. 2.2. Aspect 2

[0031] Fig. 5 shows a diagram for describing a control of the application voltage according to an aspect 2. Fig. 5 is also a graph showing a change in current density from the time of switching on to the time of stopping. The abscissa axis indicates time, and the ordinate axis indicates the current density. In the application voltage control according to aspect 2, the control device 30 controls the electric power source 29 at the times of starting and stopping the water electrolysis device 10 so that the average change rate of the current density in a range where the current density is equal to or less than 0.4 A / cm 2 is higher than in an area where the current density is higher than 0.4 A / cm 2 and is equal to or less than the current density (M) at the time of continuous operation of the water electrolysis device. The average change rate of the current density in this embodiment can be calculated as in the following description using Fig. 5 as an example. Here T 10 a start time, T 11a time at which the current density at the time of start is 0.4 A / cm 2 will, T 12 a time at which continuous operation begins after the time of start, T 13 a time immediately before the start of stopping, T 14 a time at which the current density at the time of stopping is 0.4 A / cm 2 will, and T 15 a time at which the stop is completed. - The average rate of change of the current density is in the range where the current density is equal to or less than 0.4 A / cm 2 is, in case of the time of switching on: R 11 = 0.4 / (T 11 -T 10 ) - The average rate of change of current density is in the range where the current density is higher than 0.4 A / cm 2 is, in case of the time of switching on: R 12 = (M-0.4) / (T 12 -T 11 ) - The average rate of change of current density is in the range where the current density is higher than 0.4 A / cm 2 is, in case of the time of stopping: R 13 = (M-0.4) / (T 14 -T13) - The average rate of change of the current density is in the range where the current density is equal to or less than 0.4 A / cm 2 is, in case of the time of stopping: R 14 = 0.4 / (T 15 -T 14 )

[0032] That is, R 11 > R 12 and R 14 > R 13are met. By controlling the application voltage at the times of turning on and off, it is possible to shorten the range where the current density is low and where cross leakage is likely to occur, and it is possible to limit the occurrence of cross leakage. The inventor's investigation has shown that it is possible to further restrict the occurrence of cross leakage by increasing the average change rate of the current density at least in the range where the current density is equal to or lower than 0.4 A / cm 2 is, and the time (T 10 are 11 ) of the area is shortened.

[0033] The specific value of the average change rate of the current density in the region where the current density is low (in the embodiment, the region where the current density is equal to or lower than 0.4 A / cm 2 is not particularly limited and can be 20 [A / (cm 2· second)] or higher and 500 [A / (cm 2 · second)] or lower. Since this value is higher, the range where the current density is low can be shortened. Therefore, a value of 40 [A / (cm 2 ·second)] or higher is preferable, and 90 [A / (cm 2 A time delay of 1 second or higher is even more preferable. On the other hand, the upper limit of the value is not particularly limited. There is a time delay between the command from the control device 30 and the actual voltage being reached. The higher the average change rate of the current density, the longer the delay and the larger the time gap. Therefore, the upper limit of the value can be set within a range such that the gap is not mistakenly detected as a fault (e.g., short circuit).

[0034] Between the time of switching on and the time of stopping, the value of the average rate of change may be the same or different in the area where the current density is low.

[0035] At the moment of switching on, the average rate of change of current density in the area where the current density is higher than 0.4 A / cm 2 and in which the current density is equal to or lower than M, lower than the average rate of change of the current density in the region in which the current density is equal to or lower than 0.4 A / cm 2 and therefore the time of T 11 are 12set to be somewhat long. This makes it possible to easily control the change in temperature rise that occurs behind the increase in current density, to efficiently perform water electrolysis by ensuring sufficient warm-up time, and to reduce the load on the water electrolyzer 10 from the standpoint of avoiding a sudden change. Similarly, at the time of stopping, it is possible to easily control the change in temperature drop that occurs behind the drop in current density and to reduce the load on the water electrolyzer 10 from the standpoint of avoiding a sudden change. 2.3. Aspect 3

[0036] Fig. 6 shows a diagram for describing a control of the application voltage according to an aspect 3. Fig.Figure 6 is also a graph showing a change in current density from the time of turning on to the time of stopping. The abscissa axis indicates time, and the ordinate axis indicates the current density. When controlling the applied voltage according to aspect 3, the control device 30 controls the electric power source 29 so that the current density at the time of turning on the water electrolysis device 10 becomes 0.4 A / cm within 5 seconds. 2 reached and the water electrolysis device 10 at the time of stopping the water electrolysis device 10 within 5 seconds after the current density reaches 0.4 A / cm 2 has reached the stop state.

[0037] In the embodiment, at the times of switching on and stopping, the time for a range in which the current density is equal to or higher than 0 A / cm 2 and equal to or lower than 0.4 A / cm 2within 5 seconds. This makes it possible to shorten the range where the current density is low and where cross leakage is easy to occur at the times of turning on and off, and it is possible to limit the occurrence of cross leakage. The inventor's investigation has shown that it is possible to further limit the occurrence of cross leakage by at least narrowing the range where the current density is equal to or less than 0.4 A / cm 2 is shortened.

[0038] The average rate of change of the current density in the region where the current density is low (in the embodiment, the region where the current density is equal to or lower than 0.4 A / cm 2 is not particularly limited and can be 20 [A / (cm 2 · second)] or higher and 500 [A / (cm 2· second)] or lower. Since this value is higher, the range where the current density is low can be shortened. Therefore, a value of 40 [A / (cm 2 · second)] or higher is preferable, and 90 [A / (cm 2 A time of 1 second or higher is even more preferable. On the other hand, the upper limit of the value is not particularly limited. There is a time delay between the command from the control device 30 and the actual attainment of the voltage. The higher the average change rate of the current density, the longer the delay and the larger the time gap. Therefore, the upper limit of the value can be set within a range such that the gap is not recognized as a fault (e.g., short circuit).

[0039] Between the time of switching on and the time of stopping, the value of the average rate of change may be the same or different in the area where the current density is low.

[0040] In the embodiment, at the times of switching on and stopping, the rate of change of the current density and the time in the areas where the current density is higher than 0.4 A / cm 2 is not particularly limited, and the rate of change of the current density can be maintained or changed. By setting the rate of change of the current density to a lower rate of change in the range where the current density is higher than 0.4 A / cm 2 than in the area where the current density is equal to or lower than 0.4 A / cm 2However, it is possible to easily control the change in temperature rise that occurs behind the increase in current density, to efficiently perform water electrolysis by ensuring sufficient warm-up time, and to reduce the load on the water electrolyzer 10 from the viewpoint of avoiding a sudden change. Similarly, at the time of stopping, it is possible to easily control the change in temperature drop that occurs behind the drop in current density and to reduce the load on the water electrolyzer 10 from the viewpoint of avoiding a sudden change. 3. Control (valve control) by the control device

[0041] At the time of stopping, the voltage sometimes does not decrease even if the application voltage of the power source 29 is reduced. After careful investigation, the inventor found that the reason why the voltage does not decrease at the time of stopping is that the hydrogen remains in the water electrolysis stack 20. Therefore, in the embodiment, the control device 30 lowers the hydrogen pressure of the hydrogen-side channel by operating the valve 28. This makes it possible to smoothly lower the voltage at the time of stopping.

[0042] The time at which the hydrogen pressure is reduced by operating the valve 28 is not particularly limited. The hydrogen pressure can be reduced by operating the valve 28 at the time of continuous operation before the time of stopping or before the current density reaches 0.4 A / cm 2The time of continuous operation before the time of stopping should be reduced after the current density begins to decrease.

[0043] The type of valve 28 only needs to be such that it can reduce the hydrogen pressure of the hydrogen-side channel and can be operated by the control device 30. For example, an electromagnetic valve or a control valve can be used as the valve 28. Furthermore, the hydrogen exiting the valve 28 can be released after dilution, collected in a tank or the like, or reacted with oxygen to be converted into water and heat for reuse or disposal. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2010236089

[0002] JP 2010236089 A [0002, 0003]

Claims

[1] A water electrolysis device which carries out water electrolysis in which hydrogen and oxygen are obtained by supplying water to water electrolysis cells and applying a voltage to the water electrolysis cells, the water electrolysis device comprising: a water electrolysis stack in which the water electrolysis cells are stacked; a water supply side channel through which water is supplied to the water electrolysis stack; a hydrogen-side channel through which the hydrogen produced by the water electrolysis stack is collected; an electrical power source that applies the voltage to the water electrolysis stack; and a control device that controls the application voltage of the electrical energy source, wherein at the times of turning on and stopping the water electrolysis device, the control device controls the voltage of the electric power source such that an average rate of change of a current density in a region where the current density is equal to or lower than half of a current density at a time of continuous operation of the water electrolysis device is higher than in a region where the current density is higher than half of the current density at the time of continuous operation. [2] A water electrolysis device which carries out water electrolysis in which hydrogen and oxygen are obtained by supplying water to water electrolysis cells and applying a voltage to the water electrolysis cells, the water electrolysis device comprising: a water electrolysis stack in which the water electrolysis cells are stacked; a water supply side channel through which water is supplied to the water electrolysis stack; a hydrogen-side channel through which the hydrogen produced by the water electrolysis stack is collected; an electrical power source that applies the voltage to the water electrolysis stack; and a control device that controls the application voltage of the electrical energy source, wherein at the times of switching on and stopping the water electrolysis device, the control device controls the electric power source so that an average rate of change of a current density in a range where the current density is equal to or lower than 0.4 A / cm 2 is higher than in an area where the current density is higher than 0.4 A / cm 2 and is equal to or lower than a current density at the time of continuous operation of the water electrolysis device. [3] A water electrolysis device which carries out water electrolysis in which hydrogen and oxygen are obtained by supplying water to water electrolysis cells and applying a voltage to the water electrolysis cells, the water electrolysis device comprising: a water electrolysis stack in which the water electrolysis cells are stacked; a water supply side channel through which water is supplied to the water electrolysis stack; a hydrogen-side channel through which the hydrogen produced by the water electrolysis stack is collected; an electrical power source that applies the voltage to the water electrolysis stack; and a control device that controls the application voltage of the electrical energy source, wherein the control device controls the electric power source so that a current density of 0.4 A / cm 2within 5 seconds at a time of switching on the water electrolyzer and the water electrolyzer reaches a stopped state within 5 seconds after the current density reaches 0.4 A / cm 2 at a time of stopping the water electrolysis device. [4] Water electrolysis device according to one of claims 1 to 3, wherein: the water electrolysis device comprises a valve that reduces the hydrogen pressure in the hydrogen-side channel; and at the time of stopping the water electrolysis device, the control device further performs control to operate the valve and reduce the hydrogen pressure of the hydrogen-side channel before the current density is reduced or before the current density reaches 0.4 A / cm 2 reached after the current density begins to be reduced.

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