Water electrolysis system

Abstract

To provide a water electrolysis system in which a malfunction can be detected with higher precision.SOLUTION: A water electrolysis system for obtaining hydrogen through water electrolysis using water electrolysis cells, includes a water electrolysis stack having a plurality of water electrolysis cells, a water-feeding-side path for feeding water to the water electrolysis stack, a hydrogen-side path for discharging hydrogen obtained in the water electrolysis stack, a plurality of voltage sensors that measure voltages of the respective water electrolysis cells, or voltages of units of a few water electrolysis cells, and a control device. The control device conducts computation of acquiring a voltage from each of the voltage sensors, and issuing a notification when the voltage is equal to or greater than a prescribed value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses that a water electrolysis device is provided with a control device that controls the operation of multiple PEM water electrolysis stacks, and that this control device performs calculations to determine the deterioration state from acquired resistance values ​​and temperatures, and issues a warning to level out the deterioration or to prompt replacement of stacks that have undergone reversible deterioration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-084259 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional technology can only detect deterioration that has progressed to the point where fluctuations in the resistance and temperature of the water electrolysis stack appear.

[0005] In view of the above, an object of the present disclosure is to provide a water electrolysis system that can detect malfunctions with greater accuracy. [Means for solving the problem]

[0006] The present application discloses a water electrolysis system that produces hydrogen by electrolyzing water using water electrolysis cells, the water electrolysis system including a water electrolysis stack having a plurality of water electrolysis cells, a water supply side path that supplies water to the water electrolysis stack, a hydrogen side path that discharges hydrogen produced by the water electrolysis stack, a plurality of voltage sensors that measure voltages of each of the plurality of water electrolysis cells or for each of the plurality of water electrolysis cells, and a control device, wherein the control device acquires voltages from each of the plurality of voltage sensors and performs calculations to issue an alert when the voltages are equal to or greater than a predetermined value.

[0007] When water electrolysis is performed in steady operation by the water electrolysis system, the control device may be configured to use a previously acquired IV characteristic of the water electrolysis cell as a reference and to issue a notification when a high voltage equal to or greater than a first threshold value higher than the IV characteristic is detected.

[0008] When the water electrolysis system is performing water electrolysis in steady operation, the control device may be configured to perform control to stop the water electrolysis system when a high voltage equal to or greater than a second threshold value that is higher than the first threshold value is detected.

[0009] The control device may be configured to purge a portion of the produced water from the hydrogen-side path when the voltage increases again after the voltage applied to the water electrolysis cell is reduced after water electrolysis during steady-state operation of the water electrolysis system is stopped.

[0010] When purging the produced water, the control device may be configured to control the water electrolysis stack to perform electrolysis operation. [Effects of the Invention]

[0011] According to the present disclosure, a malfunction in a water electrolysis stack can be detected more accurately and at an early stage. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a conceptual diagram illustrating the configuration of a water electrolysis system 10. [Figure 2] FIG. 2 is a conceptual diagram illustrating the configuration of the water electrolysis means 11. [Figure 3] FIG. 3 is a conceptual diagram illustrating the configuration of the water electrolysis cell 13. [Figure 4] FIG. 4 is a conceptual diagram of the computer 23 (control device 23). [Figure 5] FIG. 5 is a diagram showing the flow of control S10 during steady operation of the water electrolysis system. [Figure 6] FIG. 6 is a diagram illustrating the reference IV characteristic, the range of the first threshold value, and the range of the second threshold value. [Figure 7] FIG. 7 is a diagram showing the flow of control S20 during the process of stopping the water electrolysis system. DETAILED DESCRIPTION OF THE INVENTION

[0013] 1. Water electrolysis system configuration FIG. 1 conceptually illustrates a water electrolysis system 10 according to one embodiment. In this embodiment, the water electrolysis system 10 includes 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 to a water electrolysis stack 12 included in the water electrolysis means 11 from the water supply-side path 30, and electricity is applied to the water electrolysis stack 12, whereby the water is decomposed into hydrogen and oxygen, and the obtained hydrogen is discharged to the hydrogen-side path 40.

[0014] 1.1. Water electrolysis means In this embodiment, the water electrolysis means 11 includes a water electrolysis stack 12, a power supply 21, a cell monitor 22, and a control device 23. Each element will be described below. Figure 2 conceptually shows the configuration of the water electrolysis means 11.

[0015] 1.1.1.Water electrolysis stack The water electrolysis stack 12 is made up of a stack of multiple water electrolysis cells 13. Each water electrolysis cell 13 is a unit element for decomposing water into hydrogen and oxygen. Figure 3 shows a partial cross section of one water electrolysis cell 13. The water electrolysis cell 13 is well known, but in this embodiment it is made up of a plurality of layers, one of which is an oxygen evolution electrode (anode) and the other of which is a hydrogen evolution electrode (cathode) with a solid polymer electrolyte membrane 14 sandwiched therebetween. The material constituting the solid polymer electrolyte membrane 14 is a solid polymer material, such as a proton-conductive ion exchange membrane formed from a fluorine-based resin or a hydrocarbon-based resin material. This membrane exhibits good proton conductivity (electrical conductivity) in a wet state. More specifically, Nafion (registered trademark), which is a perfluorosulfonic acid membrane, is an example of such a membrane.

[0016] The oxygen evolution electrode (anode) comprises 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 made of an electrode catalyst containing at least one of a noble metal catalyst such as Pt, Ru, or Ir and an oxide thereof. The oxygen electrode gas diffusion layer 16 is made of a material that is gas permeable and conductive, specifically a porous conductive material made of metal fibers or metal particles. The oxygen electrode separator 17 has a flow path 17a through which the water to be supplied to the oxygen electrode gas diffusion layer 16, the generated oxygen, and excess water flow.

[0017] The hydrogen evolution electrode (cathode) is provided on the surface of the solid polymer electrolyte membrane 14 opposite to the surface on which the oxygen evolution electrode is arranged, and is provided with a hydrogen electrode catalyst layer 18, a hydrogen electrode gas diffusion layer 19, and a hydrogen electrode separator 20, in this order from the solid polymer electrolyte membrane 14 side. The hydrogen electrode catalyst layer 18 may be, for example, a layer containing Pt or the like. The hydrogen electrode gas diffusion layer 19 is made of a material that is gas permeable and conductive, specifically a porous material such as carbon cloth or carbon paper. The hydrogen electrode separator 20 is a member having a flow path 20a through which the generated hydrogen and the water accompanying it (produced water) flow.

[0018] Water (HO) supplied from the water supply side path 30 to the flow path 17a of the oxygen electrode separator 17 is converted into oxygen, electrons, and protons (H +) At this time, the protons pass through the solid polymer electrolyte membrane 14 and move to the hydrogen electrode catalyst layer 18. Meanwhile, the electrons separated at the oxygen electrode catalyst layer 15 pass through an external circuit and reach the hydrogen electrode catalyst layer 18. The protons then receive the electrons at the hydrogen electrode catalyst layer 18, generating hydrogen. The generated hydrogen and accompanying water reach the hydrogen electrode separator 20, are discharged from the flow path 20a, and move to the hydrogen-side path 40. The oxygen and excess water separated at the oxygen electrode catalyst layer 15 reach the oxygen electrode separator 17, are discharged from the flow path 17a, and move back to the water-supply-side path 30.

[0019] 1.1.2.Power supply As described above, the power supply 21 is a device that applies a voltage to the water electrolysis cell 13 to cause water electrolysis to proceed, and a power supply provided in a known water electrolysis system may be used. However, in this embodiment, the power supply 21 is capable of communicating with the control device 23 so that the application of voltage can be controlled by the control device 23.

[0020] 1.1.3. Cell Monitor The cell monitor 22 is a means for measuring the voltage applied to the water electrolysis cell 13. There are no particular limitations on the means as long as it can measure the voltage of the water electrolysis cell 13, and any known means can be used, such as a voltage sensor. The cell monitor 22 may measure the voltage of each of the multiple water electrolysis cells 13, or 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 voltages assumed to be applied to each water electrolysis cell 13 are averaged depending on the number of cells, which may result in a decrease in accuracy. Therefore, it is most preferable to measure the voltage of each water electrolysis cell 13, and when measuring the voltage of two or more water electrolysis cells together, it is preferable to measure five or fewer cells at a time. The cell monitor 22 is configured to be communicable so that the obtained voltage data can be converted into a signal and transmitted to the control device 23 .

[0021] 1.1.4.Controller The control device 23 is a device that controls the water electrolysis system 10. The type of the control device 23 is not particularly limited, but it can typically be configured by a computer. Figure 4 conceptually shows an example configuration of the computer 23 serving as the control device 23.

[0022] The computer 23 includes a CPU (Central Processing Unit) 23a which is a processor, a RAM (Random Access Memory) 23b which functions as a working area, a ROM (Read-Only Memory) 23c which is a storage medium, a receiving unit 23d which is an interface that accepts information into the computer 23 whether wired or wireless, and an output unit 23e which is an interface that sends information from the computer 23 to the outside whether wired or wireless. The receiver 23d is communicatively connected to the cell monitor 22, and is configured to receive the voltage of the water electrolysis cell 13 as a signal. On the other hand, the power supply 21 is communicably connected to the output unit 23e, and is configured to be able to control the voltage applied to the water electrolysis cell 13.

[0023] The computer 23 stores a computer program for executing specific commands representing each process for controlling the water electrolysis system 10. In the computer 23, the CPU 23a, RAM 23b, and ROM 23c, which serve as hardware resources, work together with the computer program. Specifically, the CPU 23a executes the computer program stored in the ROM 23c in the RAM 23b, which functions as a work area, based on a signal representing the voltage of the water electrolysis cell 13, which is obtained from the cell monitor 22 via the receiving unit 23d. Information obtained or generated by the CPU 23a is stored in the RAM 23b. Based on the obtained results, the CPU 23a transmits commands via the output unit 23e as necessary. The specific control of the water electrolysis system 10 will be described later.

[0024] 1.2.Water supply route (oxygen route) The water supply path (oxygen path) 30 is a path including piping for supplying water to the water electrolysis cells 13 of the water electrolysis stack 12 to obtain oxygen. In this embodiment, water is supplied to the water electrolysis stack 12 by a pump 31 in the water supply line 30. If necessary, a cooler for cooling the water or an ion exchanger for removing ions contained in the water may be disposed between the pump 31 and the water electrolysis stack 12. In the water supply line 30, oxygen generated in the water electrolysis stack 12 and unused water are discharged from the water electrolysis stack 12 and supplied to the gas-liquid separator 32. The gas-liquid separator 32 separates the water and oxygen, and the separated oxygen is discharged while the water is supplied again to the pump 31. Note that a pump 33 supplies insufficient water to the gas-liquid separator 32. The above-mentioned devices are connected by piping to form a fluid path. In addition to the above, known devices may also be arranged in the water supply path 30 as needed.

[0025] 1.3. Hydrogen pathway The hydrogen-side path 40 is a path including piping for extracting hydrogen separated in the water electrolysis stack 12. In the hydrogen-side path 40, hydrogen and water discharged from the water electrolysis cells 13 of the water electrolysis stack 12 are supplied to a gas-liquid separator 41. The gas-liquid separator 41 separates the water from the hydrogen. 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 is reused. At this time, the water may be passed through an ion separator before reaching the gas-liquid separator 32, if necessary. In the hydrogen-side path, these devices are connected by piping. In addition to the above, known devices may also be arranged in the hydrogen-side path 40 as needed.

[0026] 2. Control of water electrolysis systems 2.1. During electrolysis operation The performance of a water electrolysis system is affected by the characteristics of the water electrolysis cells, and continued use of deteriorated water electrolysis cells can result in increased power consumption during hydrogen production due to overvoltage. To avoid this situation, the control device 23 detects and controls a state in which the voltage of the water electrolysis cell 13 exceeds a preset voltage based on the voltage obtained from the cell monitor 22. Figure 5 shows the flow of control S10 during electrolysis operation (normal hydrogen production operation). As can be seen from Figure 5, control S10 includes steps S11 to S17. In this embodiment, the computer program stored in the control device 23 is configured to provide specific computer instructions for executing each step of control S10.

[0027] 2.1.1. Process S11 In step S11, the power supply 21 applies a voltage to the water electrolysis cell 13 to start operation, and then the preparatory operation stage ends, and the system enters a normal electrolysis operation state.

[0028] 2.1.2. Process S12 In step S12, the cell monitor 22 acquires the voltage of the water electrolysis cell 13. Here, the voltage is acquired from each of the multiple voltage sensors. The acquired voltage data is sent to the control device 23 as a signal. As described above, in this embodiment, the voltage of each of the plurality of water electrolysis cells 13 or for each of the plurality of water electrolysis cells is obtained, and the voltage of the water electrolysis cell 13 is obtained for each stacking position.

[0029] 2.1.3. Process S13 In step S13, it is determined whether the voltage of each water electrolysis cell obtained in step S12 exceeds a reference value. Here, the reference value is the previously obtained current density (A / cm 2 The reference voltage is determined from the voltage (V / cell) of each electrolysis cell relative to the total voltage (IV characteristics). When measuring the voltage of multiple electrolysis cells at once, the voltage is calculated by dividing the measured voltage by the number of electrolysis cells. Figure 6 shows an example of this IV characteristic. The range of the electrolysis cell voltage below the solid line marked A in Figure 6 is the reference voltage. In step S13, if the voltage of the water electrolysis cell 13 satisfies the reference value, the water electrolysis cell 13 is deemed to be free from deterioration or failure, and therefore the result is No, and the process returns to step S12. For the water electrolysis cell 13 whose voltage exceeds the reference value in step S13, the determination is Yes, and the process proceeds to step S14.

[0030] 2.1.4. Process S14, process S15 In step S14, for each electrolysis cell whose voltage exceeds the reference value in step S13, it is determined whether the voltage is within the first threshold range. The first threshold range is a voltage range in which the electrolysis cell is suspected to be degraded but has not yet reached a level that would require the entire water electrolysis system to be shut down. This is the voltage range of the electrolysis cell between the solid line and the dashed line indicated by B in Figure 6.

[0031] For a water electrolysis cell whose voltage is within the first threshold range in step S14, the determination is Yes, and the process proceeds to step S15, where a notification is issued that an overvoltage within the first threshold range has occurred in that water electrolysis cell. The notification method is not particularly limited, and examples include displaying on an image display device (not shown) a message indicating that an overvoltage within the first threshold range has occurred and location information (e.g., ID) of the water electrolysis cell. Alternatively, or in addition to, a sound or audio notification may also be issued.

[0032] For water electrolysis cells whose voltages exceed the first threshold range in step S14, the result is No, and the process proceeds to step S16.

[0033] 2.1.5. Process S16 In step S16, a notification is issued for any water electrolysis cell 13 whose voltage is higher than the first threshold range in step S14, indicating that the voltage has reached the second threshold range. The second threshold range is an overvoltage range in which the water electrolysis cell is estimated to be at a fault level and the entire water electrolysis system must be shut down. This range is the region in which the water electrolysis cell voltage is higher than the dashed line indicated by C in FIG. 6 . In step S16, a notification is issued that an overvoltage of the second threshold has occurred in the water electrolysis cell 13. The method of notification is not particularly limited, and examples include displaying on an image display device (not shown) a message indicating that an overvoltage in the second threshold range has occurred and location information (e.g., ID) of the water electrolysis cell. Alternatively, or in addition to, a sound or audio notification may be issued. After the notification is given, the process proceeds to step S17.

[0034] 2.1.6. Process S17 In step S17, in response to the fact that a water electrolysis cell 13 has failed in step S16, the operation of the water electrolysis system 10 is stopped. The water electrolysis process can be stopped in the usual manner, and the application of voltage from the power supply 21 is stopped.

[0035] 2.2.Stop processing The shutdown process, as described in step S17, can be performed normally. However, if there is no produced water on the hydrogen generating electrode side of the water electrolysis cell during the shutdown process, a fuel cell reaction (power generation reaction) may occur in the water electrolysis cell, which may cause deterioration of the catalyst in the hydrogen electrode catalyst layer. Therefore, in this embodiment, the shutdown process also monitors whether a fuel cell reaction is occurring, and if it does occur, performs processing to quickly resolve the reaction. Figure 7 shows the flow of control S20 for the shutdown process. As can be seen from Figure 7, control S20 includes steps S21 to S25.

[0036] 2.2.1. Process S21 In step S21, the hydrogen-side path is purged. Produced water is discharged from the hydrogen-side path by purging from any position in the hydrogen-side path. This reduces the hydrogen pressure on the hydrogen generating electrode side of the water electrolysis cell 13. The produced water is purged while applying a voltage to the water electrolysis cell 13 from the power source 21, with the current density set to 0.5 A / cm. 2 Electrolysis is performed under conditions that do not cause hydrogen cross-leakage of a certain level or more (or minimize hydrogen generation), and the time is short, on the order of a few seconds to a few minutes. This purging of the produced water from the hydrogen generation electrode can suppress the occurrence of the above-mentioned fuel cell reaction. This purging can be performed by controlling a solenoid valve (not shown) provided in the hydrogen side path with the control device 23. At this time, an inert gas such as nitrogen may be injected into the hydrogen electrode generating electrode side of the water electrolysis stack 13.

[0037] 2.2.2. Process S22 In step S22, the water feed-side path is purged. Purging the water feed-side path discharges oxygen from the water feed-side path. Specifically, for example, the control device 23 sends pure water to the water electrolysis stack 13 using the pump 31, and discharges oxygen remaining in the water electrolysis stack 13 as a result of water electrolysis to the gas-liquid separator 32. This reduces the oxygen pressure on the oxygen evolving electrode side of the water electrolysis cell 13.

[0038] 2.2.3. Process S23 In step S23, the cell monitor 22 acquires the voltage of the water electrolysis cell 13. In this embodiment, the voltage is acquired from each of the multiple voltage sensors. The acquired voltage data is sent to the control device 23 as a signal. As described above, in this embodiment, the voltage is acquired for each of the plurality of water electrolysis cells 13 or for each of the plurality of water electrolysis cells, and the voltage is acquired for each stacking position of the water electrolysis cells 13.

[0039] 2.3.4. Process S24 In step S24, it is determined whether the voltage of the water electrolysis cell 13 obtained in step S23 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 from the voltage of the water electrolysis cell 13. That is, if a voltage increase (e.g., 0.1 V to 1.0 V per water electrolysis cell) is detected again during the shutdown process, it can be determined that the reaction is occurring. Therefore, in step S24, if the voltage of the water electrolysis cell 13 acquired in step S23 is equal to or lower than the set voltage, the result is Yes because the voltage is normal, and the process proceeds to step S25. On the other hand, if the voltage of the water electrolysis cell 13 acquired in step S23 is greater than the set voltage, it is determined as No because the cell is not normal and a fuel cell reaction is occurring, and the process proceeds to step S21 to perform purging again.

[0040] 2.3.5. Process S25 In step S25, if it is determined in step S24 that the voltage is normal, it is determined whether to complete monitoring. Completion of monitoring is determined based on whether the shutdown process of the water electrolysis system 10 has been completed. If it has been completed, the process returns to Yes and ends. On the other hand, if the shutdown process has not been completed, the process returns to step S23 and continues monitoring.

[0041] Other During shutdown processing, if there is a cross leak or a short circuit in the water electrolysis cell 13, a sudden drop in the voltage of the water electrolysis cell is observed immediately after the application of voltage from the power supply 21 is stopped for shutdown. For this reason, the device may be configured to notify the user if the voltage of the water electrolysis cell falls below a threshold within a certain period of time after the application of voltage from the power supply 21 is stopped.

[0042] 3. Effects etc. The water electrolysis system 10 and the control S10 thereof according to this embodiment enable early detection of deterioration of the water electrolysis cells 13 and facilitate identification of deteriorated water electrolysis cells 13, thereby enabling more accurate detection of malfunctions and enabling prompt shutdown of the water electrolysis system 10 as needed, which can also be performed during the electrolysis reaction. When control S20 is used, deterioration of the water electrolysis cells while the water electrolysis system 10 is stopped can be suppressed. [Explanation of symbols]

[0043] 10...water electrolysis device, 12...water electrolysis stack, 13...water electrolysis cell, 21...power supply, 22...cell monitor (voltage sensor), 23...control device, 30...water supply side path (oxygen side path), 40...hydrogen side path

Claims

1. A water electrolysis system for obtaining hydrogen by electrolyzing water using a water electrolysis cell, a water electrolysis stack including a plurality of the water electrolysis cells; a water supply side path for supplying water to the water electrolysis stack; a hydrogen-side path for discharging the hydrogen obtained in the water electrolysis stack; a plurality of voltage sensors that measure voltages of the plurality of water electrolysis cells or for each of the plurality of water electrolysis cells; a control device; the control device acquires voltages from each of the plurality of voltage sensors; When water electrolysis is performed in steady operation by the water electrolysis system, the control device performs a calculation using a previously acquired I-V characteristic of the water electrolysis cell as a reference, and issues a notification when a high voltage equal to or greater than a first threshold value higher than the I-V characteristic is detected. Water electrolysis system.

2. 2. The water electrolysis system according to claim 1, wherein, when the water electrolysis system is performing steady-state operation of water electrolysis, the control device performs control to stop the water electrolysis system when a high voltage equal to or greater than a second threshold value that is higher than the first threshold value is detected.

3. 3. The water electrolysis system according to claim 1, wherein, when a voltage increase occurs again after water electrolysis during steady-state operation of the water electrolysis system is stopped and the voltage applied to the water electrolysis cell is reduced, the control device purges a portion of the produced water from the hydrogen-side path.

4. The water electrolysis system according to claim 3 , wherein the control device controls the water electrolysis stack to perform an electrolysis operation when the produced water is purged.

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