Water electrolysis system

Abstract

To provide a water electrolysis system capable of more accurately detecting a trouble in a water electrolysis cell.SOLUTION: The water electrolysis system electrolyzing water using water electrolysis cells to obtain hydrogen, comprises a water electrolysis stack comprising a plurality of water electrolysis cells, a water supply route supplying the water electrolysis stack with water, a hydrogen route discharging the hydrogen obtained in the water electrolysis stack, a plurality of voltage sensors measuring the voltage of each of the plurality of water electrolysis cells or the voltage of each group of a plurality of water electrolysis cells, and a controller which acquires a voltage from each of the plurality of voltage sensors to carry out calculation to make notification when any of the voltages is below a predetermined value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a water electrolysis system.

Background Art

[0002] Patent Document 1 discloses that a water electrolysis apparatus includes a control device that controls the operation of a plurality of PEM water electrolysis stacks, and this control device performs an operation to determine the deterioration state from the acquired resistance value and temperature, and issues a warning to promote the leveling of deterioration and the replacement of stacks in which reversible deterioration has progressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the prior art, only deterioration that has become large enough for fluctuations to appear in the resistance value and temperature of the water electrolysis stack can be detected.

[0005] In view of the above, an object of the present disclosure is to provide a water electrolysis system that can detect problems more accurately. [[ID=4))

Means for Solving the Problems

[0006] The present application discloses a water electrolysis system that obtains hydrogen by electrolyzing water with a water electrolysis cell, including a water electrolysis stack having a plurality of water electrolysis cells, a water supply side path for supplying water to the water electrolysis stack, a hydrogen side path for discharging hydrogen obtained in the water electrolysis stack, a plurality of voltage sensors for measuring the voltage of each of the plurality of water electrolysis cells or for each of the plurality of water electrolysis cells, and a control device. The control device acquires the voltage from each of the plurality of voltage sensors and performs an operation to notify when the voltage is lower than a predetermined value.

[0007] The predetermined value may be the voltage value obtained by the equivalent circuit of the water electrolysis cell.

[0008] The calculation may be performed when the water electrolysis system starts up, and the control device may be configured to compare a predetermined value, which is the normal water electrolysis cell voltage corresponding to the current, with the voltage obtained from the voltage sensor, and determine that a short circuit abnormality has occurred if the voltage is lower than the allowable voltage.

[0009] The calculation is performed during steady-state operation of the water electrolysis system, and the control device may be configured to determine a short-circuit abnormality when it detects a voltage lower than the lower limit of the width of the IV characteristics of the water electrolysis cell, which has predetermined values ​​acquired in advance, as a reference. [Effects of the Invention]

[0010] According to this disclosure, malfunctions in the water electrolysis stack can be detected more accurately and at an earlier stage. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a conceptual diagram illustrating the configuration of the water electrolysis system 10. [Figure 2] Figure 2 is a conceptual diagram illustrating the configuration of the water electrolysis means 11. [Figure 3] Figure 3 is a conceptual diagram illustrating the configuration of the water electrolysis cell 13. [Figure 4] Figure 4 is a conceptual diagram of the computer 23 (control device 23). [Figure 5] Figure 5 shows the flow of control S10 during the electrolysis operation of a water electrolysis system. [Figure 6] Figure 6 illustrates the equivalent circuit of a water electrolysis cell. [Figure 7] Figure 7 illustrates the relationship between the calculated voltage and the measured voltage. [Figure 8] Figure 8 illustrates the IV characteristics of a water electrolysis cell. [Figure 9] Figure 9 shows the flow of control S30 during the shutdown process of the water electrolysis system.

Embodiments for Carrying out the Invention

[0012] 1. Configuration of the water electrolysis system FIG. 1 conceptually shows a water electrolysis system 10 according to one embodiment. In this embodiment, the water electrolysis system 10 has a water electrolysis means 11, a water supply side path (oxygen side path) 30, and a hydrogen side path 40. In the water electrolysis system 10, water is supplied from the water supply side path 30 to the water electrolysis stack 12 provided in the water electrolysis means 11 and energized to decompose water into hydrogen and oxygen, and hydrogen is obtained and discharged to the hydrogen side path 40.

[0013] 1.1. Water electrolysis means In this embodiment, the water electrolysis means 11 includes a water electrolysis stack 12, a power source 21, a cell monitor 22, and a control device 23. Hereinafter, each element will be described. FIG. 2 conceptually shows the configuration of the water electrolysis means 11.

[0014] 1.1.1. Water electrolysis stack The water electrolysis stack 12 is formed by stacking a plurality of water electrolysis cells 13. The water electrolysis cell 13 is a unit element for decomposing water into hydrogen and oxygen. FIG. 3 shows a part of the cross section of one water electrolysis cell 13. The water electrolysis cell 13 is as known. In this embodiment, it is composed of a plurality of layers, with one side being an oxygen generation electrode (anode) and the other side being a hydrogen generation electrode (cathode) sandwiching a solid polymer electrolyte membrane 14. The material constituting the solid polymer electrolyte membrane 14 is a solid polymer material, and examples thereof include a proton-conductive ion exchange membrane formed of a fluorine-based resin, a hydrocarbon-based resin material, or the like. This exhibits good proton conductivity (electrical conductivity) in a wet state. More specifically, Nafion (registered trademark), which is a perfluorosulfonic acid membrane, can be mentioned.

[0015] The oxygen generation electrode (anode) includes an oxygen electrode catalyst layer 15, an oxygen electrode gas diffusion layer 16, and an oxygen electrode separator 17 in this order from the solid polymer electrolyte membrane 14 side. The oxygen electrode catalyst layer 15 is a layer comprising an electrode catalyst containing at least one noble metal catalyst such as Pt, Ru, or Ir, and its oxide. The oxygen electrode gas diffusion layer 16 is composed of a material that is gas permeable and conductive. Specifically, a porous conductive material made of metal fibers or metal particles can be used. The oxygen electrode separator 17 is equipped with a channel 17a through which water supplied to the oxygen electrode gas diffusion layer 16, the generated oxygen, and excess water flow.

[0016] The hydrogen generation electrode (cathode) is provided on the side of the solid polymer electrolyte membrane 14 opposite to the side where the oxygen generation electrode is located, and the hydrogen electrode catalyst layer 18, the hydrogen electrode gas diffusion layer 19, and the hydrogen electrode separator 20 are provided in this order from the solid polymer electrolyte membrane 14 side. The hydrogen electrode catalyst layer 18 can be a layer containing, for example, Pt. The hydrogen electrode gas diffusion layer 19 is composed of a material that is gas permeable and conductive. Specifically, this can include porous materials such as carbon cloth or carbon paper. The hydrogen electrode separator 20 is a component equipped with a channel 20a through which the generated hydrogen and the accompanying water flow.

[0017] Water (H2O) supplied from the water supply path 30 to the flow path 17a of the oxygen electrode separator 17 is energized by the power supply 21 between the oxygen generation electrode and the hydrogen generation electrode, causing oxygen, electrons, and protons (H2O) to be generated in the oxygen electrode catalyst layer 15 under an applied potential. + It is decomposed into ). At this time, the protons move through the solid polymer electrolyte membrane 14 to the hydrogen electrode catalyst layer 18. Meanwhile, the electrons separated in the oxygen electrode catalyst layer 15 move through the external circuit to the hydrogen electrode catalyst layer 18. There, the protons receive electrons in the hydrogen electrode catalyst layer 18 and hydrogen is generated. The generated hydrogen and the accompanying water reach the hydrogen electrode separator 20 and are discharged from the channel 20a, moving to the hydrogen side path 40. The oxygen separated in the oxygen electrode catalyst layer 15 and excess water reach the oxygen electrode separator 17 and are discharged from the channel 17a, moving back to the water supply side path 30.

[0018] 1.1.2.Power supply The power supply 21 is a device that applies voltage to the water electrolysis cell 13 to carry out water electrolysis, as described above, and can be any power supply that is included in a known water electrolysis system. However, in this embodiment, the power supply 21 is made capable of communicating with the control device 23 so that the voltage application can be controlled by the control device 23.

[0019] 1.1.3. Cell Monitor The cell monitor 22 is a means for measuring the voltage applied to the water electrolysis cell 13. Specifically, it is not limited to any known device that can measure the voltage of the water electrolysis cell 13, and such a device can be used, for example, a voltage sensor. The cell monitor 22 may measure the voltage of each of the multiple water electrolysis cells 13, or it may measure the voltage of two or more water electrolysis cells 13 together. However, when measuring the voltage of two or more water electrolysis cells 13 together, the voltage applied to each water electrolysis cell 13 is averaged according to the number of cells grouped together, which may lead to a decrease in accuracy. Therefore, it is most preferable to obtain the voltage of each water electrolysis cell 13, and when obtaining the voltage of two or more water electrolysis cells together, it is preferable to limit the number to five or less. Alternatively, the voltage of only the water electrolysis cells at both ends of the stacking direction, where abnormalities are easily detected, may be obtained individually, and the voltage of two or more water electrolysis cells placed in between may be obtained together. The cell monitor 22 is configured to communicate so that it can transmit the acquired voltage data as a signal to the control device 23.

[0020] 1.1.4. Control Device The control device 23 is a device that controls the water electrolysis system 10. The configuration of the control device 23 is not particularly limited, but it can typically be configured as a computer. Figure 4 conceptually shows an example of the configuration of a computer 23 as the control device 23.

[0021] The computer 23 includes a CPU (Central Processing Unit) 23a which is a processor, RAM (Random Access Memory) 23b which functions as a work area, ROM (Read-Only Memory) 23c as a storage medium, a receiving unit 23d which is an interface for receiving information into the computer 23 whether wired or wireless, and an output unit 23e which is an interface for sending information from the computer 23 to the outside whether wired or wireless. The receiving unit 23d is connected to the cell monitor 22 in a communication manner and is configured to receive the voltage of the water electrolysis cell 13 as a signal. On the other hand, the output unit 23e is connected to the power supply 21 in a communication manner and is configured to control the voltage applied to the water electrolysis cell 13.

[0022] Computer 23 stores computer programs that define each process for controlling the water electrolysis system 10 as a specific command and execute it. In computer 23, the CPU 23a, RAM 23b, and ROM 23c, which are hardware resources, work together with the computer programs. Specifically, the CPU 23a performs its function by executing the computer program recorded in ROM 23c in RAM 23b, which functions as a work area, based on a signal representing the voltage of the water electrolysis cell 13 acquired from the cell monitor 22 via the receiving unit 23d. Information acquired or generated by the CPU 23a is stored in RAM 23b. Then, based on the obtained results, commands are transmitted via the output unit 23e as needed. The specific control details of the water electrolysis system 10 will be explained later.

[0023] 1.2. Water supply path (oxygen path) The water supply route (oxygen route) 30 is a route that includes piping for supplying water to the water electrolysis cells 13 of the water electrolysis stack 12 in order to obtain oxygen. In this configuration, the water supply path 30 is supplied with water to the water electrolysis stack 12 by a pump 31. If necessary, a cooler to cool the water and an ion exchanger to remove ions contained in the water may be placed between the pump 31 and the water electrolysis stack 12. In the water supply path 30, oxygen generated in the water electrolysis stack 12 and unused water are further discharged from the water electrolysis stack 12 and supplied to the gas-liquid separator 32. In the gas-liquid separator 32, water and oxygen are separated, the separated oxygen is discharged, and the water is supplied back to the pump 31. Any insufficient water is supplied to the gas-liquid separator 32 from the pump 33. The above-mentioned devices are connected by piping, forming a fluid path. In addition to the above, known devices may be placed in the water supply path 30 as needed.

[0024] 1.3. Hydrogen-side pathway The hydrogen-side path 40 is a path that includes piping for extracting hydrogen separated in the water electrolysis stack 12. In the hydrogen-side path 40, hydrogen and water (associated water) discharged from the water electrolysis cells 13 of the water electrolysis stack 12 are supplied to the gas-liquid separator 41. In the gas-liquid separator 41, water and hydrogen are separated. The hydrogen separated in the gas-liquid separator 41 is dehumidified or otherwise stored in a tank. The water separated in the gas-liquid separator 41 is sent by a pump 42 to the gas-liquid separator 32 in the water supply-side path 30 and reused. This water may be passed through an ion separator before reaching the gas-liquid separator 32 if necessary. In the hydrogen side path, each of these devices is connected by piping. In addition to the above, known devices may be placed in the hydrogen side path 40 as needed.

[0025] 2. Control of the water electrolysis system The performance of a water electrolysis system depends on the characteristics of the water electrolysis cell, and continuing to use a degraded water electrolysis cell will increase power consumption in hydrogen production. To avoid this situation, the control device 23 performs control by comparing the voltage of the water electrolysis cell 13 obtained from the cell monitor 22 with preset characteristics. This will be explained in detail below.

[0026] 2.1. During electrolytic operation (at startup and during steady-state operation) Examples of situations in which a voltage is applied to a water electrolysis cell and water electrolysis is performed while the system is running (electrolysis operation) include the start of operation of the water electrolysis system 10 (from startup to steady-state operation) and during steady-state operation. When the water electrolysis system 10 starts up, the water electrolysis stack 12 needs to inject charge into the water electrolysis cells, which have a large capacitance capacity due to their structure, and charge them up to the electrolysis potential. This charging is preferably done rapidly because if it is done slowly, cross-leakage (where hydrogen generated on the hydrogen generation electrode side of the water electrolysis cell leaks to the oxygen generation electrode side) is likely to occur. On the other hand, if there is a possibility of a malfunction such as a short circuit in the water electrolysis cell 13, rapid charging should be avoided. Therefore, in this embodiment, when starting up (from the start of the water electrolysis system until steady-state operation), the current is rapidly increased while monitoring whether there is a voltage drop that indicates a short circuit in the estimated cell voltage calculated by a charging voltage simulation based on the capacitance of the water electrolysis cell set in advance, and an abnormality is determined. On the other hand, after the voltage of the water electrolysis cell reaches the voltage for steady-state operation during charging at the start of operation, degradation is determined by comparing the measured voltage with a preset normal IV characteristic. The following examples illustrate this point.

[0027] Figure 5 shows the flow of control S10 of the water electrolysis system 10 during electrolysis operation in one configuration. As can be seen from Figure 5, control S10 has processes S11 to S22. In this configuration, the computer program stored in the control device 23 described above is configured to become the specific commands to the computer for executing each process of control S10.

[0028] 2.1.1. Process S11 In process S11, a voltage is applied to the water electrolysis cell 13 by the power supply 21. This voltage application is carried out as predetermined, increasing the voltage in a time series at the start of operation, and maintaining the steady-state operating voltage after it reaches the steady-state operating voltage. Therefore, in control S10, when voltage application starts in process S11, the voltage is controlled by the control device 23 as predetermined, unless the stop process S18 described later occurs.

[0029] 2.1.2. Process S12 In process S12, the voltage of the water electrolysis cell 13 is acquired by the cell monitor 22. Here, the voltage is acquired for each of the multiple voltage sensors. The acquired voltage data is transmitted as a signal to the control device 23. As described above, in this embodiment, the voltage is acquired for each of the multiple water electrolysis cells 13, or for each of the multiple water electrolysis cells, and the voltage of the water electrolysis cells 13 is acquired for each stacking position.

[0030] 2.1.3. Process S13 In process S13, it is determined from the voltage obtained in process S12 whether charging is currently underway (i.e., whether it is the start of operation). Since the voltage has not yet reached the voltage of steady-state operation during charging, it is possible to determine whether charging is underway from the voltage value. If the voltage has not yet reached the voltage for steady-state operation, it is considered the start of operation, so the answer is Yes and the process proceeds to S19. On the other hand, if the voltage has reached the voltage for steady-state operation, the answer is No and the process proceeds to S14.

[0031] 2.1.4. Process S19 In process S19, if it was determined in process S13 that the device is currently charging, a calculation is performed to determine if the voltage is at a normal value. The means for determining whether the voltage is at a normal value are not particularly limited, but for example, it can be done as follows. Figure 6 shows the equivalent circuit of the water electrolysis cell 13 during charging. In Figure 6, R Mem R is the proton transfer resistance of the solid polymer electrolyte membrane 14. CL C is catalytic reaction resistance. CLV represents the electrical double-layer capacitance. According to this equivalent circuit, the voltage V applied to the water electrolysis cell during charging is cell The current consumption of the water electrolysis cell is I cell In this case, it can be expressed by the following equation (1), and this voltage can be treated as a normal value.

[0032]

number

[0033] Figure 7 shows, as an example, a comparison of the measured voltage of the water electrolysis cell with the calculated voltage of the water electrolysis cell obtained by the equivalent circuit of equation (1) at different time intervals. As can be seen from Figure 7, the voltage calculated by the equivalent circuit is consistent with the actual voltage. Furthermore, by setting a certain tolerance range for the error in the calculated voltage, it is possible to determine whether the voltage of the water electrolysis cell at that time is normal based on the value calculated by the equivalent circuit.

[0034] Thus, in process S19, the voltage of the water electrolysis cell, which is at a normal value, is compared with the voltage of the water electrolysis cell obtained in process S12. Although the above explains how to obtain normal values ​​through equivalent circuit calculations, this is not limited to this method. Alternatively, the normal voltage corresponding to the current, which has been obtained in advance through tests, etc., can be stored in the control device 23 as a database, for example as a mapping, and this can be compared with the measured value as the normal value.

[0035] 2.1.5. Process S20, process S21 In process S20, based on the comparison in process S19, it is determined whether the voltage of the water electrolysis cell at the start of operation is within the normal range. In particular, if the voltage of the water electrolysis cell obtained in process S12 is lower than the normal range compared to the normal voltage, there is a high possibility of a short circuit in the water electrolysis cell, and it is preferable to avoid continuing to apply voltage in this case. On the other hand, if the voltage is higher than a certain range, it is preferable to suspect a malfunction in the cell monitor and prompt inspection.

[0036] In process S20, if the voltage of the water electrolysis cell obtained in process S12 is within the normal range, the response is "Yes" and the process returns to S12. On the other hand, if the voltage of the water electrolysis cell obtained in process 12 is outside the normal range in process S20, the result is "No" and the process proceeds to process 21 for notification. After notification in process S21, the process proceeds to process S18 for stop processing. Process S18 will be explained later. Here, the method of notification in process S21 is not particularly limited, but for example, an image display device (not shown) may display that a malfunction has occurred in the water electrolysis cell 13 and the location information (ID, etc.) of the water electrolysis cell. In addition to or in addition to this, notification by sound or voice may also be provided.

[0037] 2.1.6. Process S14 In process S14, based on the determination in process S13 that the water electrolysis system 10 has completed its startup phase and entered steady-state operation, the voltage of each water electrolysis cell obtained in process S12 is used to calculate whether the voltage of each water electrolysis cell exceeds a reference value. Here, the reference value is the "current density (A / cm²)" which has been obtained in advance. 2 The determination is made from the "Voltage per water electrolysis cell (V / cell)" (IV characteristic) relative to the total voltage. If the voltage of multiple water electrolysis cells is measured together, the obtained voltage is divided by the number of water electrolysis cells combined. Figure 8 shows one example of the IV characteristic. Here, the range between the dashed line and the solid line shown as A in Figure 8 is the reference voltage. A voltage lower than this, in range B, suggests a short circuit problem within the water electrolysis cell, and a voltage higher than this, in range C, suggests an overvoltage problem, raising concerns about deterioration of the water electrolysis cell.

[0038] 2.1.7. Process S15 In process S15, based on the comparison in process S14, it is determined whether the voltage of the water electrolysis cell during steady-state operation is within the normal range. As mentioned above, if the voltage of the water electrolysis cell obtained in process S12 is lower than the normal range compared to the voltage within the reference range, there is a high possibility of a short circuit in the water electrolysis cell, and it is preferable to avoid continuing to apply voltage. On the other hand, if the voltage of the water electrolysis cell obtained in process S12 is higher than the normal range, there is concern about deterioration of the water electrolysis cell, and depending on the degree of deterioration, it is preferable to avoid continuing to apply voltage. In process S15, if the voltage of the water electrolysis cell 13 meets the standard value, it is considered that there is no deterioration or malfunction in the water electrolysis cell 13, so the answer is Yes, and the process returns to S12. If the voltage of a water electrolysis cell 13 falls outside the range of the reference value in process S15, the result is "No," and the process proceeds to process S16.

[0039] 2.1.8. Process S16, Process S17, Process S22 In process S16, it is determined whether the water electrolysis system 10 needs to be stopped for the water electrolysis cells whose voltage was outside the range of the reference value in process S15 and was therefore marked as No. If the voltage of the water electrolysis cell falls below the reference range, a short circuit in the water electrolysis cell is suspected as described above, and it is better to stop the water electrolysis system, so the answer is Yes, and the process proceeds to S17, where this is reported, and then to S18. The notification in S17 can be considered in the same way as in S21 above.

[0040] On the other hand, when the voltage of the water electrolysis cell falls above the standard range, deterioration of the water electrolysis cell is presumed, as described above. Since deterioration of the water electrolysis cell does not necessarily require the immediate shutdown of the water electrolysis system, it is preferable to set a threshold. That is, at voltages that do not exceed the threshold, deterioration of the water electrolysis cell is presumed, but it is considered that the voltage is not severe enough to shut down the entire water electrolysis system, so the result is "No" in process S16, and after notification in process S22, the process returns to S12. The notification in process S22 at this time is not particularly limited, but it can state that there is deterioration, but it is not necessary to shut down the water electrolysis system. The method of notification can be considered in the same way as in process S21 described above. In contrast, if the voltage exceeds the threshold, it is presumed that the degradation is significant and has reached a failure level. Therefore, in order to stop the water electrolysis system, the system is prompted to respond with "Yes" in process S16, proceeding through process S17 to process S18. The specific value of the threshold here is not particularly limited, and any threshold obtained experimentally can be used.

[0041] 2.1.9. Process S18 In process S18, upon receiving a determination that the water electrolysis system should be stopped, the operation of the water electrolysis system 10 is stopped. The water electrolysis process can be stopped as usual, and the application of voltage from the power supply 21 is stopped.

[0042] 2.2. Stopping Process As described in process S18 above, the shutdown process can be carried out as usual. However, if the hydrogen generation electrode side of the water electrolysis cell is not accompanied by associated water during the shutdown process, a fuel cell reaction (power generation reaction) may occur in the water electrolysis cell, which can degrade the catalyst in the hydrogen electrode catalyst layer. Therefore, in this embodiment, the shutdown process is further monitored to see if a fuel cell reaction is occurring, and if it does, a process is performed to quickly resolve it. Figure 9 shows the flow of the shutdown process control S30. As can be seen from Figure 9, control S30 includes processes S31 to S35.

[0043] 2.2.1. Process S31 In process S31, the hydrogen-side path is purged. Purging the hydrogen-side path discharges the associated water from it. In this embodiment, the control device 23 opens a valve (not shown) provided in the hydrogen-side path, purging the associated water from the hydrogen-side path. This reduces the hydrogen pressure on the hydrogen generation electrode side of the water electrolysis cell 13. Here, the purging of the associated water is performed while applying voltage to the water electrolysis cell 13 with the power supply 22, and at this time the current density is set to 0.5 A / cm². 2 The following conditions are met during electrolysis: the operation is performed under conditions where no hydrogen cross-leakage occurs (or the minimum amount of hydrogen is generated), and the duration is short, ranging from a few seconds to a few minutes. This purging of the accompanying water at the hydrogen electrode can suppress the occurrence of the fuel cell reaction described above. Furthermore, this process may be carried out while injecting an inert gas such as nitrogen into the hydrogen electrode generation side of the water electrolysis stack 13.

[0044] 2.2.2. Process S32 In process S32, the water supply path is purged. Purging the water supply path removes oxygen from the water supply path. The control device 23 sends pure water to the water electrolysis stack 13 using the pump 31, and the oxygen remaining in the water electrolysis stack 13 during water electrolysis is discharged to the gas-liquid separator 32. This reduces the oxygen pressure on the oxygen generation electrode side of the water electrolysis cell 13.

[0045] 2.2.3. Process S33 In process S33, the voltage of the water electrolysis cell 13 is acquired by the cell monitor 22. In this embodiment, the voltage is acquired for each of the multiple voltage sensors. The acquired voltage data is transmitted as a signal to the control device 23. As described above, in this embodiment, a voltage is acquired for each of the multiple water electrolysis cells 13, or for each of the multiple water electrolysis cells, and a voltage is acquired for each stacking position of the water electrolysis cells 13.

[0046] 2.3.4. Process S34 In process S34, it is determined whether the voltage of the water electrolysis cell 13 obtained in process S33 is normal. As described above, if a fuel cell reaction (power generation reaction) occurs in the water electrolysis cell during the shutdown process, the catalyst in the hydrogen electrode catalyst layer may deteriorate. Whether this fuel cell reaction is occurring can be determined by the voltage of the water electrolysis cell 13. That is, if a voltage (re-increase) of a predetermined voltage (for example, 0.1V to 1.0V per water electrolysis cell) or higher is detected during the shutdown process, it can be determined that the reaction is occurring. Therefore, in process S34, if the voltage of the water electrolysis cell 13 obtained in process S33 is less than or equal to the set voltage, it is considered a normal voltage and the process proceeds to process S35. On the other hand, if the voltage of the water electrolysis cell 13 obtained in process S33 is greater than the set voltage, it is considered abnormal and a fuel cell reaction is occurring, so the process proceeds to process S31 and hydrogen-side path purging is performed again.

[0047] 2.3.5. Process S35 In process S35, it is determined whether to complete monitoring when it was determined in process S34 that the voltage is normal. Completion of monitoring is determined by whether the shutdown process of the water electrolysis system 10 has been completed. If it has been completed, the response is Yes and the process ends. On the other hand, if the shutdown process has not been completed, the response is No and the process returns to process S33, and monitoring continues.

[0048] 2.3.6. Others During the shutdown process, if there is a cross leak or short circuit in the water electrolysis cell 13, a rapid drop in the voltage of the water electrolysis cell will be observed immediately after the voltage application by the power supply 21 is stopped for shutdown. Therefore, it is also possible to configure the system to notify if the voltage of the water electrolysis cell falls below a threshold voltage within a certain period of time after the voltage application by the power supply 21 is stopped.

[0049] 3. Effects, etc. According to this embodiment of the water electrolysis system 10 and its control S10, malfunctions in the water electrolysis cells 13, such as short circuits, can be detected at an early stage, making it easier to identify the malfunctioning water electrolysis cell 13. This allows for more accurate detection of malfunctions, and the water electrolysis system 10 can be quickly shut down if necessary. Furthermore, this can be done during the electrolysis reaction. When control S30 is used, it is possible to suppress the deterioration of the water electrolysis cell while the water electrolysis system 10 is stopped. [Explanation of symbols]

[0050] 10...Water electrolysis unit, 12...Water electrolysis stack, 13...Water electrolysis cell, 21...Power supply, 22...Cell monitor (voltage sensor), 23...Control device, 30...Water supply path (oxygen path), 40...Hydrogen path

Claims

1. A water electrolysis system that obtains hydrogen by electrolyzing water using a water electrolysis cell, A water electrolysis stack having a plurality of the water electrolysis cells, A water supply path for supplying water to the water electrolysis stack, A hydrogen side path for discharging the hydrogen obtained from the water electrolysis stack, Multiple voltage sensors that measure the voltage of each of the multiple water electrolysis cells, or for each of the multiple water electrolysis cells, A control device is provided, The control device acquires voltage from each of the plurality of voltage sensors and performs a calculation to notify when the voltage is lower than the voltage value obtained by the equivalent circuit of the water electrolysis cell. Water electrolysis system.

2. The water electrolysis system according to claim 1, wherein the calculation is performed when the water electrolysis system starts operation, and the control device compares the voltage value obtained by the equivalent circuit of the water electrolysis cell with the voltage obtained from the voltage sensor as the normal water electrolysis cell voltage corresponding to the current which has been acquired in advance, and determines that a short circuit abnormality has occurred if the voltage is lower than the allowable voltage.

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