Water electrolysis system and method for detecting abnormalities in a water electrolysis system

Abstract

To detect anomalies in a water electrolysis cell without complicated configuration.SOLUTION: A control unit of a water electrolysis system includes: acquiring a voltage of a water electrolysis cell after the operation of the water electrolysis is stopped; and determining that anomalies occur at least in one of a micro short circuit and a pinhole, when a voltage drop time tc being a time from the stop of the operation of the water electrolysis up until the voltage of the water electrolysis cell drops to zero, is shorter than a time ta shown in the expression (1) as follows. (Here, Vc represents a volume of a flow path on a hydrogen electrode side of the water electrolysis cell, and Fw represents an amount of accompaniment water per unit time in the water electrolysis cell with rated operation.)SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This disclosure relates to a water electrolysis system and a method for detecting abnormalities in a water electrolysis system. [Background technology]

[0002] Conventionally, a type of water electrolysis device that produces hydrogen and oxygen by the electrolysis of water is known as a polymer electrolyte water electrolysis device (PEM type water electrolysis device). A PEM type water electrolysis device is a membrane electrode assembly in which electrodes are bonded to both sides of a solid polymer electrolyte membrane. The PEM-type water electrolysis apparatus includes a water electrolysis cell containing a MEA (Metal Energy Electrolyte). It is known that problems such as damage to the electrolyte membrane can occur with use in such PEM-type water electrolysis apparatuses. For example, it is known that "microshorts" can occur in which fibers constituting the gas diffusion layer contained in the electrodes formed on the electrolyte membrane penetrate the electrolyte membrane. It is also known that when such microshorts occur, pinholes are formed in the electrolyte membrane at the points where the fibers penetrate. The formation of pinholes in the electrolyte membrane progresses due to microshorts, but can also occur due to various reasons that cause deterioration of the electrolyte membrane even when microshorts do not occur.

[0003] To address such problems, for example, Patent Document 1 discloses a technique in which, while a PEM-type water electrolysis stack, which is a stack of water electrolysis cells, is stopped, a specific voltage is applied to the water electrolysis cells using an auxiliary power supply different from the main power supply used for water electrolysis to detect the cell current, and it is determined that a micro-short has occurred when the cell resistance value calculated from these voltage and current values ​​is below a threshold value. Furthermore, Patent Document 2 discloses a technique in which, after stopping the main power supply, a pinhole detection voltage is applied between the anode and cathode of the electrolytic cell using an auxiliary power supply, and the presence or absence of a pinhole is determined by comparing the detected voltage with a threshold voltage. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-196906 [Patent Document 2] Japanese Patent Publication No. 2006-138004 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, in the water electrolysis systems described in References 1 and 2, it was necessary to apply a voltage for abnormality detection to the water electrolysis device using an auxiliary power supply different from the main power supply when water electrolysis using the main power supply was stopped, in order to detect the occurrence of microshorts and pinholes. Furthermore, in the water electrolysis system of Reference 2, although the presence or absence of pinholes could be determined, it was not possible to detect microshorts that did not lead to pinhole formation. Therefore, there was a need for a technology that could detect the occurrence of microshorts and pinholes in water electrolysis cells without complicating the configuration by providing an auxiliary power supply or similar. [Means for solving the problem]

[0006] This disclosure can be implemented in the following forms: (1) According to one embodiment of the present disclosure, a water electrolysis system is provided. The water electrolysis system comprises a water electrolysis cell comprising a solid polymer electrolyte membrane and a pair of electrodes arranged on both sides of the electrolyte membrane, which generates hydrogen and oxygen by electrolysis of water; a power supply device for applying a voltage to the water electrolysis cell; a voltage sensor for detecting the voltage of the water electrolysis cell; and a control unit, wherein the control unit stops the operation of water electrolysis involving the application of voltage from the power supply device to the water electrolysis cell. Later, the voltage of the water electrolysis cell detected by the voltage sensor is obtained, and the voltage drop time tc from the time the water electrolysis operation stops until the voltage of the water electrolysis cell becomes 0 is given by the time t shown in equation (1) below. aWhen the time is shorter than this, it is determined that an abnormality, including at least one of a microshort and a pinhole, has occurred in the electrolyte membrane.

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Equation

Equation

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[0007] [Figure 1]An explanatory diagram showing the schematic configuration of the water electrolysis system of the first embodiment. [Figure 2] A schematic cross-sectional diagram showing the structure of a water electrolysis cell. [Figure 3] A flowchart illustrating the abnormality detection processing routine. [Figure 4] A schematic diagram illustrating how the cell voltage decreases after water electrolysis is stopped. [Figure 5] A flowchart illustrating the abnormality detection processing routine. [Figure 6] A flowchart illustrating the abnormality detection processing routine. [Figure 7] This diagram illustrates a model of how the cell voltage decreases after water electrolysis is stopped. [Modes for carrying out the invention]

[0008] A. First Embodiment: (A-1) Configuration of the water electrolysis system: Figure 1 is an explanatory diagram showing the schematic configuration of a water electrolysis system 10, which is one embodiment of the present disclosure. Figure 2 is a schematic cross-sectional view showing the configuration of a water electrolysis cell 22 that constitutes a cell stack 20 of the water electrolysis system 10. The water electrolysis system 10 of this embodiment produces hydrogen and oxygen by electrolyzing water. The water electrolysis system 10 comprises a cell stack 20, a power supply 30, a cell monitor 32, a water supply unit 40, and a control unit 70.

[0009] The cell stack 20 is a polymer electrolyte membrane (PEM) type water electrolysis device, and has a structure in which multiple water electrolysis cells 22, in which the electrolysis of water takes place, are stacked. As shown in Figure 2, the water electrolysis cell 22 has a stacked structure comprising an electrolyte membrane 80, a pair of electrodes, an oxygen electrode 81 and a hydrogen electrode 82, which are placed on both sides of the electrolyte membrane 80, an anode diffusion layer 83 placed on the outside of the oxygen electrode 81 (the side away from the electrolyte membrane 80), a separator 85 placed on the outside of the anode diffusion layer 83, a cathode diffusion layer 84 placed on the outside of the hydrogen electrode 82, and a separator 86 placed on the outside of the cathode diffusion layer 84.

[0010] The electrolyte membrane 80 is a membrane made of a solid polymer material that exhibits proton (hydrogen ion) conductivity in a wet state, such as perfluorocarbon sulfonic acid polymer. The oxygen electrode 81 is equipped with a catalyst such as iridium oxide and a solid polymer electrolyte, and the hydrogen electrode 82 is equipped with a catalyst such as platinum and a solid polymer electrolyte. The anode diffusion layer 83 and the cathode diffusion layer 84 are made of a conductive porous material, such as titanium fibers. The separators 85 and 86 are made of a gas-impermeable conductive material and are placed between adjacent water electrolysis cells 22. An anode-side channel 87 is formed between the separator 85 and the oxygen electrode 81, and a cathode-side channel 88 is formed between the separator 86 and the hydrogen electrode 82. Figure 2 shows how groove structures for forming the anode-side channel 87 or the cathode-side channel 88 are formed on the surfaces of the separators 85 and 86 facing the electrodes. The anode-side channel 87 or the cathode-side channel 88 may be constructed with a structure different from the groove structure described above. For example, a porous body may be placed between the separator and the diffusion layer, and the channel may be formed by the voids within this porous body.

[0011] When performing electrolysis of water, a voltage is applied from the power supply 30 to the cell stack 20 (see Figure 1). Figure 2 schematically shows the voltage application as a relationship between the power supply 30 and the water electrolysis cell 22. When a voltage is applied to the water electrolysis cell 22 while water is supplied to the anode-side channel 87 by the water supply unit 40, the supplied water is electrolyzed at the oxygen electrode 81 to produce hydrogen ions and oxygen. The configuration of the water supply unit 40 will be explained in detail later. The hydrogen ions produced at the oxygen electrode 81 move along with water (hereinafter also called "associated water") through the electrolyte membrane 80 towards the hydrogen electrode 82. At the hydrogen electrode 82, hydrogen is produced when the hydrogen ions that have moved through the electrolyte membrane 80 combine with electrons.

[0012] Furthermore, various configurations can be adopted for the power source 30. The power source 30 may be a power source derived from renewable energy such as solar, hydroelectric, wind, wave, biomass, or geothermal energy, or it may be a commercial power source.

[0013] Returning to Figure 1, a cell monitor 32 is attached to the cell stack 20. The cell monitor 32 only needs to have the function of a "voltage sensor" that detects the voltage of each water electrolysis cell 22. In this embodiment, the cell monitor 32 is connected to the output terminal of each water electrolysis cell 22, and when performing the electrolysis of water, it detects the output voltage and output current of each water electrolysis cell 22 to monitor the status of water electrolysis proceeding in each water electrolysis cell 22.

[0014] The water supply unit 40 includes a pure water tank 41 and an anode-side gas-liquid separator 42. The water stored in the pure water tank 41 is supplied to the cell tower via the anode-side gas-liquid separator 42, as will be described later. The oxygen is supplied to the cell stack 20 and used for the electrolysis of water. During the electrolysis of water, the oxygen generated at the oxygen electrode 81, along with some of the water that was not electrolyzed, is discharged from the cell stack 20 to the anode discharge channel 54 via the anode-side flow path 87. The anode-side discharge channel 54 connects the outlet of the flow path where each anode-side flow path 87 in the cell stack 20 converges to the anode-side gas-liquid separator 42. The oxygen and water discharged from the cell stack 20 to the anode-side discharge channel 54 are separated into oxygen and water in the anode-side gas-liquid separator 42. The oxygen separated in the anode-side gas-liquid separator 42 is sent to the outside of the water electrolysis system 10 via the oxygen discharge channel 55.

[0015] The anode-side gas-liquid separator 42 is connected to the pure water tank 41 by a supply channel 50. A supply pump 43 is provided in the supply channel 50, and by driving the supply pump 43, pure water is supplied from the pure water tank 41 to the anode-side gas-liquid separator 42. The anode-side gas-liquid separator 42 and the inlet of the channels branching to each anode-side channel 87 in the cell stack 20 are connected by a circulation channel 52 equipped with a circulation pump 44. By driving the circulation pump 44, the water separated from oxygen in the anode-side gas-liquid separator 42, as described above, is supplied to the anode-side channel 87 in each water electrolysis cell 22 via the circulation channel 52, along with the water supplied from the pure water tank 41 to the anode-side gas-liquid separator 42, and is used again for electrolysis.

[0016] During the electrolysis of water, the hydrogen produced at the hydrogen electrode 82, along with the accompanying water that has moved to the hydrogen electrode 82 through the electrolyte membrane 80 along with the hydrogen ions, is discharged from the cell stack 20 to the cathode-side discharge channel 62. The cathode-side discharge channel 62 connects the outlet of the channel where each cathode-side channel 88 in the cell stack 20 converges to the cathode-side gas-liquid separator 60. After the hydrogen discharged from the cell stack 20 to the cathode-side discharge channel 62 is separated from the water in the cathode-side gas-liquid separator 60 and then discharged to the hydrogen discharge channel 63. The hydrogen discharged to the hydrogen discharge channel 63 may be stored in a hydrogen tank, for example, or sent to a hydrogen consumption device that uses hydrogen as an energy source.

[0017] The control unit 70 is a so-called microcomputer equipped with a CPU, ROM, RAM, etc., and controls the operation of each part of the water electrolysis system 10. The control unit 70 acquires detection signals from sensors and the like provided in each part of the water electrolysis system 10, including the cell monitor 32, and drives and controls each part, including the pumps provided in each flow path. The control performed by the control unit 70 includes control of each part of the water electrolysis system 10 when performing water electrolysis, as well as control related to abnormality detection performed when stopping the operation of water electrolysis.

[0018] The program that implements the above-mentioned anomaly detection control may be pre-stored in the control unit 70. Alternatively, the program may be provided by the program provider via a communication network. Furthermore, the program may be stored on a commercially available and distributed portable storage medium. In this case, the portable storage medium may be set in an external or built-in reader, and the program may be read and executed by the control unit 70. Various types of storage media can be used as portable storage media, such as CD-ROMs, DVD-ROMs, flexible disks, optical disks, magneto-optical disks, IC cards, and USB memory devices.

[0019] (A-2) Detection of abnormalities in the water electrolysis system: Figure 3 is a flowchart showing the abnormality detection processing routine executed in the control unit 70. The control unit 70 detects abnormalities related to microshorts and pinholes when the water electrolysis operation stops. The abnormality detection processing routine in Figure 3 is activated in the water electrolysis system 10 when the water electrolysis operation stops. At the time the water electrolysis operation stops, the application of voltage to the cell stack 20 by the power supply 30 is stopped. At this time, the anode-side channel 87 is filled with water, and the cathode-side channel 88 is filled with hydrogen. When the voltage application to the cell stack 20 is stopped and the electrolysis of water is stopped, the circulation of water to the anode-side channel 87 may be stopped at the same time. However, after the above stopping operation, the circulation of water to the anode-side channel 87 may be continued for, for example, several tens to several hundreds of seconds.

[0020] When this routine is started, the CPU of the control unit 70 acquires a detection signal from the cell monitor 32 and starts monitoring the voltage of each water electrolysis cell 22 (step S100). Then, for each water electrolysis cell 22 that makes up the cell stack 20, the time t from the time water electrolysis stops until the cell voltage becomes 0 is measured. c Obtain the value (step S110). Hereafter, the time from the cessation of water electrolysis until the cell voltage becomes 0 will also be referred to as the "voltage drop time".

[0021] Here, the cell voltage of the water electrolysis cell 22 becomes 1.48V, which is the voltage corresponding to the thermodynamic equilibrium potential of water electrolysis (the theoretical electrolysis voltage plus a voltage corresponding to the enthalpy change), when the water electrolysis operation stops, and then gradually decreases. In step S110, the voltage drop is monitored for each water electrolysis cell 22 constituting the cell stack 20, and the voltage drop time t until the cell voltage drops to 0 is measured for each water electrolysis cell 22. c Obtain it.

[0022] In step S110, for each water electrolysis cell 22, the voltage drop time t until the cell voltage drops to 0 is c Upon obtaining this, the CPU of the control unit 70 determines the voltage drop time t of each water electrolysis cell 22. c And, a predetermined reference time t a This is compared with the water electrolysis cells 22 that make up the cell stack 20, and the voltage drop time t c is the reference time t a It is determined whether or not there is a water electrolysis cell 22 with a shorter time than this (step S120). a This will be explained in more detail later.

[0023] Voltage drop time t c is the reference time t a If it is determined that there are no water electrolysis cells 22 with a shorter voltage drop time than t (step S120: NO), the CPU of the control unit 70 determines that there are no water electrolysis cells 22 with abnormalities (step S130) and terminates this routine. c is the reference time t a If it is determined that there is a water electrolysis cell 22 with a shorter voltage drop time than t (step S120: YES), the CPU of the control unit 70 will determine that there is an abnormality, i.e., the voltage drop time t c is the reference time t a In the water electrolysis cell 22, which has a shorter duration than t, it is determined that an abnormality including at least one of a microshort and a pinhole has occurred (step S140), and this routine is terminated. Below, the reference time t a I will explain this.

[0024] Figure 4 is a schematic diagram illustrating the decrease in cell voltage after the water electrolysis operation is stopped. In Figure 4, graph α shows the voltage drop in a normal water electrolysis cell 22. Figure 4 shows the voltage drop time t from the stop of water electrolysis until the cell voltage becomes 0 in a normal water electrolysis cell 22. c to, time t α This is shown as follows: If there is no abnormality in the water electrolysis cell 22, the rate at which the cell voltage decreases after electrolysis stops is determined according to the electrolyte membrane characteristics of the water electrolysis cell 22 and the operating state before electrolysis stops, and the voltage drop time t from the stop of water electrolysis until the cell voltage becomes 0 is determined. c This value will be approximately constant depending on the size and operating conditions before electrolysis is stopped, as described above.

[0025] The inventors of this application conducted an experiment in which they repeatedly performed the operation and stopping of water electrolysis using a cell stack 20 composed of water electrolysis cells 22 without abnormalities, that is, a cell stack 20 composed of water electrolysis cells 22 in which the voltage drops when electrolysis is stopped in the same pattern as in graph α. Specifically, after starting the water electrolysis system 10, they performed the operation of water electrolysis for 2 hours under the specified rated operating conditions for the cell stack 20, and then stopped the operation, repeating this process. As a result, among the water electrolysis cells 22 constituting the cell stack 20, as shown in graphs β and γ in Figure 4, the voltage drop until the cell voltage becomes 0 between t c However, the initial time t α A water electrolysis cell 22 appeared in which the voltage drop time t in the water electrolysis cell 22 was shorter than that of a normal water electrolysis cell 22, that is, the rate at which the cell voltage decreases after water electrolysis stops is faster than that of a normal water electrolysis cell 22. In Figure 4, the voltage drop time t in the water electrolysis cell 22 shown in graph β is observed. c to β This is shown as follows, and the voltage drop time t in the water electrolysis cell 22 shown in graph γ c to γ This is shown as (however, tγ <tβ)。

[0026] As described above, if the operation of repeatedly electrolyzing water and stopping continues, the voltage drop time t will be as shown in graph β.c Among the water electrolysis cells 22, which have a relatively small degree of shortening, as shown in graph γ, the voltage drop time t c In this way, the degree of shortening of the voltage drop time t has become relatively large. c ga t α When a gas leak check was performed on the electrolyte membrane 80 of the shortened water electrolysis cell 22, the voltage drop time t was as shown in graph β. c In the water electrolysis cell 22, where the degree of shortening was relatively small, no gas leak was detected. Separately, as shown in graph γ, the voltage drop time t c Gas leaks were detected in some of the water electrolysis cells 22 where the degree of shortening was relatively large. The gas leak check was performed by pressurizing and sealing one of the anode-side flow path 87 or cathode-side flow path 88 with nitrogen gas and observing the subsequent pressure drop in the pressurized and sealed flow path.

[0027] From these results, as shown in graph β, the voltage drop time t c In water electrolysis cells 22 where the degree of shortening is relatively small and no gas leak occurs, it is thought that a micro-short (hereinafter also referred to as "micro-short anomaly") occurs in the electrolyte membrane 80, where fibers constituting the gas diffusion layer penetrate the electrolyte membrane 80. In such water electrolysis cells 22, conductive fibers that penetrate or deeply penetrate the electrolyte membrane 80 short-circuit the oxygen electrode 81 and the hydrogen electrode 82, accelerating the decrease in cell voltage after water electrolysis stops, and the voltage drop time t c It is thought that this has been shortened. However, it is difficult to directly determine whether a micro-short is actually occurring, and in this embodiment, as described above, the voltage drop time t until the cell voltage becomes 0 is considered to be shortened. c The phenomenon of shortening of the voltage drop time t indicates that an abnormality has occurred where the conductivity between the oxygen electrode 81 and the hydrogen electrode 82 has increased due to conductive fibers, etc., and a microshort is detected. Therefore, in this embodiment, a "microshort abnormality" refers not only to cases where conductive fibers completely penetrate the electrolyte membrane 80, but also to cases where conductive fibers pierce the electrolyte membrane 80, increasing the conductivity between the electrodes and shortening the voltage drop time t. cThe length is shortened, but the conductive fibers do not completely penetrate the electrolyte membrane 80, which may include an abnormality as a precursor to a microshort.

[0028] Also, as shown in graph γ, the voltage drop time t c In the water electrolysis cell 22 where the degree of shortening was relatively large and a gas leak was detected, it is thought that a pinhole (hereinafter also referred to as "pinhole anomaly") has occurred in the electrolyte membrane 80. In such a water electrolysis cell, water moves from the anode-side channel 87 to the cathode-side channel 88 through the pinhole formed in the electrolyte membrane 80, and the hydrogen in the anode-side channel 87 is replaced by the moved water, causing the electrode potential of the hydrogen electrode 82 to decrease, which further accelerates the decrease in the cell voltage after water electrolysis stops, and the voltage drop time t c It is thought that the voltage drop time t was shortened. And, as shown in graph β, c Among the water electrolysis cells 22, which have a relatively small degree of shortening, as shown in graph γ, the voltage drop time t c Since some cells exhibited a relatively large degree of shortening, it is considered that at least some of the water electrolysis cells 22 that experienced pinhole abnormalities originated from water electrolysis cells 22 that experienced microshort abnormalities. However, it is also possible that the water electrolysis cells 22 determined to have experienced pinhole abnormalities as described above may include those that developed pinhole abnormalities due to causes other than microshort abnormalities.

[0029] Based on the above, in step S120 of Figure 3, the voltage drop time t is used to detect the water electrolysis cell 22 in which an abnormality including at least one of a microshort and a pinhole has occurred. c The reference value is the reference time t shown in the following formula (1). a I set it.

[0030]

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[0031] However, in the above formula (1), V c [cm3 ] is the volume of the flow path on the hydrogen electrode 82 side in the water electrolysis cell 22, that is, the volume of the cathode side flow path 88, and F w [cm 3 [ / sec] is the amount of associated water per unit time in the water electrolysis cell 22 operating at rated capacity. The reference time t is expressed by equation (1). a This corresponds to the time required to replace the hydrogen filling the cathode-side channel 88 with water and fill the cathode-side channel 88 with water, when the same amount of water as the amount of associated water moving in the electrolyte membrane 80 during rated operation is supplied to the cathode-side channel 88.

[0032] In a normal water electrolysis cell 22, when water electrolysis stops, hydrogen moves from the cathode-side channel 88 to the anode-side channel 87 by diffusion within the electrolyte membrane 80, and the amount of hydrogen in the cathode-side channel 88 decreases, causing the cell voltage to drop. In contrast, if an abnormality occurs due to a pinhole or microshort, the time it takes for the cell voltage to drop is shortened due to hydrogen replacement by water movement through the pinhole or short circuit. However, predicting the shortened time due to these abnormal phenomena is extremely difficult. Specifically, for example, the time required for the voltage drop due to water movement caused by pinhole formation is, in principle, calculated using the above equation (1), the amount of associated water F per unit time during rated operation. w Instead, it is considered that the formula should be defined by the product of the amount of circulating water F1 on the oxygen electrode 81 side and the rate z of water moving to the hydrogen electrode 82 side through a pinhole. However, in practice, it is not practical to calculate the above z from pinholes that occur unexpectedly. The inventors of this application have established a criterion for determining that the cell voltage is decreasing at a rate that does not occur in a normal water electrolysis cell 22, that is, a criterion for determining an abnormality that includes at least one of microshorts and pinholes, as shown in the above formula (1) time t a We found that this can be used. This standard is also applicable when water is circulated on the hydrogen electrode side.

[0033] In equation (1), the volume V of the cathode-side flow path 88 is... cFor example, if the cathode-side channel 88 is configured with a groove structure as shown in Figure 2, the volume of the space formed between the surface of the separator 86 and the hydrogen electrode 82 can be calculated based on the size of the groove structure formed on the surface of the separator 86 (width, depth, length, etc.). Alternatively, if a porous body is placed between the separator 86 and the hydrogen electrode 82, the volume of the space inside the porous body can be calculated based on the external dimensions and porosity of the porous body to determine the volume V of the cathode-side channel 88. c We just need to find the following. Also, in equation (1), the amount of associated water F per unit time in the water electrolysis cell 22 performing rated operation. w To detect abnormalities, the cell stack 20, which is the target of the abnormality detection, can be operated at its rated capacity, and the accompanying water volume per unit time can be experimentally measured in advance. The above accompanying water volume F w This can be calculated by measuring the amount of water added per unit time in the cathode-side gas-liquid separator 60 of the water electrolysis system 10 when water electrolysis is performed under rated operating conditions, and dividing this by the number of water electrolysis cells 22 that make up the cell stack 20. In this case, the amount of water added per unit time in the cathode-side gas-liquid separator 60 may be corrected by estimating the losses due to evaporation etc. in the cathode-side gas-liquid separator 60.

[0034] As previously described, the operation of repeatedly electrolyzing water and stopping continues, while the reference time t shown in Figure 3 is maintained. a When abnormality detection is performed using this method, the voltage drop time t until the cell voltage becomes 0 is determined. c is the reference time t a A water electrolysis cell 22 with a shorter voltage drop time t appeared. Furthermore, when the operation of repeatedly performing water electrolysis and stopping was continued, the above-mentioned voltage drop time t c is the reference time t a In over 90% of water electrolysis cells 22, the voltage drop time t was shorter than that of the water electrolysis cell 22. c The time was shortened even further. Water electrolysis and stopping were repeated. During the experiment in which the operation continues, the voltage drop time t c is the reference time t a Of the water electrolysis cells 22 whose voltage drop time t has been shortened, cthat is relatively long and the voltage drop time t c that is relatively short were randomly selected and leak checks were performed. As a result, no gas leak was detected for those with a relatively long voltage drop time t c whereas gas leaks were detected for those with a relatively long voltage drop time t c From the above, it is considered that by performing the determination shown in FIG. 3 using the reference time t a of Expression (1), it is possible to determine that at least one of the micro short circuit abnormality and the pinhole abnormality has occurred.

[0035] Here, the rate of decrease in the cell voltage after the stop of water electrolysis can vary depending on various conditions related to the configuration of the water electrolysis cell 22, such as the electrolyte membrane characteristics in the water electrolysis cell 22, for example. In the present embodiment, using Expression (1), the volume V c of the cathode side flow path 88 and the amount of accompanying water F w per unit time in the water electrolysis cell 22 operating at rated operation are used to derive the reference time t a and abnormality determination is performed using this. Therefore, even when the conditions related to the water electrolysis cell 22, such as the size of each part of the water electrolysis cell 22 and the configuration of the electrolyte membrane 80, are different, it is possible to set an appropriate reference time t a .

[0036] For example, as an example, when the volume V c of the cathode side flow path 88 is 2.8 cm 3 and the measured value of the amount of accompanying water F w per unit time in the water electrolysis cell 22 operating at rated operation is 5 cm 3 / min, the reference time t a obtained from Expression (1) is 0.56 minutes (34 seconds). For such a water electrolysis cell 22, an experiment was conducted in which the operations of water electrolysis and stop were repeated continuously, and the voltage drop time t c (t α ) until the cell voltage at the beginning of the experiment in such a water electrolysis cell 22 reached 0 was 112 seconds. For a cell stack 20 including such a water electrolysis cell 22, an experiment was conducted to continue the operation of repeating water electrolysis and stop, and the voltage drop time t c until the cell voltage reached 0 was the reference time t aOf the water electrolysis cells 22 whose voltage drop time t has been shortened, c Those with a relatively long voltage drop time t c We randomly select those with relatively short voltage drop times t c The average value was calculated. As a result, the voltage drop time t c Although the voltage drop time t is relatively long c (t β The voltage drop time t was 28 seconds. c Although the voltage drop time is relatively short t c (t γ The time was 11 seconds, and gas leaks were detected in all of these water electrolysis cells 22.

[0037] According to the water electrolysis system 10 of this embodiment configured as described above, the voltage drop time t until the cell voltage becomes 0 after the water electrolysis operation stops is c However, the reference time t shown in equation (1) a In cells where the voltage has decreased below a certain level, it is determined that an abnormality, including at least one of micro-shorts and pinholes, has occurred. Therefore, without complicating the system configuration by, for example, providing a special configuration for abnormality detection such as an auxiliary power supply, it is possible to detect abnormalities, including at least one of micro-shorts and pinholes, through the simple operation of detecting the cell voltage after the water electrolysis has stopped. When a cell monitor 32 is used to monitor the operation of each water electrolysis cell 22 during the water electrolysis operation in order to detect the cell voltage of the water electrolysis cell 22 after the water electrolysis has stopped, it is desirable because there is no need to provide an additional device to detect the cell voltage for abnormality detection. The abnormality determination method in this embodiment can detect abnormalities, including at least one of micro-shorts and pinholes, with high accuracy, especially when stopping after performing water electrolysis under conditions close to the rated operating conditions.

[0038] In this embodiment, after stopping water electrolysis, the voltage of all water electrolysis cells 22 constituting the cell stack 20 was detected using the cell monitor 32 to determine whether or not an abnormality had occurred. However, a different configuration is also possible. For example, if certain locations in the cell stack 20 are known to be particularly prone to micro-short and pinhole abnormalities, the presence or absence of an abnormality may be determined only for the water electrolysis cells 22 included in those locations.

[0039] B. Second Embodiment: Figure 5 is a flowchart showing the abnormality detection processing routine executed in the control unit 70 of the water electrolysis system of the second embodiment. The water electrolysis system of the second embodiment has the same configuration as the water electrolysis system 10 of the first embodiment. The abnormality detection processing routine of the second embodiment is executed at the same timing as the abnormality detection processing routine of the first embodiment, but in place of the abnormality detection processing routine of the first embodiment. The differences from the first embodiment will be described below.

[0040] In the abnormality detection processing routine of the second embodiment, steps S100 to S130 are executed in the same manner as in the first embodiment. In step S120, the voltage drop time t c is the reference time t a If it is determined that there is a water electrolysis cell 22 with a shorter voltage drop time t (step S120: YES), the CPU of the control unit 70 determines that there is a water electrolysis cell 22 with a shorter voltage drop time t c is the reference time t a For each of the water electrolysis cells 22 (water electrolysis cells 22 having an abnormality including at least one of a microshort and a pinhole, hereinafter also referred to as an "abnormal cell"), the voltage drop time t is defined as follows: c However, the predetermined standard time t p It is determined whether or not the voltage drop time t is shorter than (step S150). Then, the CPU of the control unit 70 determines among the abnormal cells the voltage drop time t c is the reference time t pIf no abnormal cells exist with a voltage drop time shorter than t (step S150: NO), then all abnormalities in the abnormal cells are determined to be micro-short abnormalities (step S160), and this routine is terminated. Also, among the abnormal cells, the voltage drop time t c is the reference time t p If there is a water electrolysis cell 22 with a shorter voltage drop time t (step S150: YES), c is the reference time t p An abnormality occurring in a water electrolysis cell 22 that is shorter than the specified value is determined to be a pinhole abnormality (step S170), and this routine is terminated. In step S170, any abnormalities occurring in the remaining abnormal cells are determined to be microshort abnormalities.

[0041] Here, the reference time t used in step S150 p is the reference time t a It is predetermined as a shorter time than the standard time t. p As a result of continuing the repeated operation of water electrolysis and stopping as described in the first embodiment, the voltage drop time t is as shown in graph γ. c The degree of shortening becomes relatively large, and the voltage drop time t of the water electrolysis cell 22 in which a gas leak was detected by the gas leak check becomes relatively large. c You can set it using this. Specifically, the reference time t p For example, the voltage drop time t is as described above. c The degree of shortening was relatively large, indicating a gas leak in the voltage drop time t of the water electrolysis cell 22. c It can be the minimum of these values. Alternatively, the voltage drop time t of the water electrolysis cell 22 in which a gas leak was detected as described above. c The average value may be used. Considering the desired accuracy when detecting pinhole anomalies, the reference time t p You can set it as appropriate.

[0042] With this configuration, in addition to the same effects as in the first embodiment, it becomes possible to accurately detect pinhole anomalies, which require a higher degree of urgency for abnormality countermeasures, in distinction from micro-short anomalies. To accurately determine whether or not a pinhole anomaly has actually occurred, further gas leak checks can be performed, but as shown in Figure 5, by pre-determining whether a pinhole anomaly has occurred and narrowing down the water electrolysis cells 22 that should be subjected to gas leak checks, the number of water electrolysis cells 22 that should be subjected to gas leak checks can be reduced.

[0043] C. Third Embodiment: In the first and second embodiments, the cell monitor 32 detects the voltage of each water electrolysis cell 22 constituting the cell stack 20, but a different configuration is also possible. In the following, as a third embodiment, a cell stack 20 in which multiple water electrolysis cells 22 are stacked is divided into cell groups consisting of n water electrolysis cells 22 arranged in series and connected in a continuous manner, and a configuration in which the cell monitor 32 detects the voltage for each cell group is described.

[0044] Figure 6 shows the abnormality determination process performed in the control unit 70 of the water electrolysis system of the third embodiment. This is a flowchart representing the routine. The water electrolysis system of the third embodiment has the same configuration as the water electrolysis system 10 of the first embodiment, except that the cell stack 20 is divided into cell groups composed of n consecutive water electrolysis cells 22, and the cell monitor 32 detects the voltage of each cell group. The abnormality detection processing routine of the third embodiment is executed at the same timing as the abnormality detection processing routine of the first embodiment, but in place of the abnormality detection processing routine of the first embodiment. The differences from the first embodiment will be described below.

[0045] When this routine is started when the water electrolysis operation stops, the CPU of the control unit 70 acquires a detection signal from the cell monitor 32 and starts monitoring the voltage of each cell group (hereinafter also referred to as "group voltage") (step S200). Then, for each cell group constituting the cell stack 20, the voltage drop time t from the time the water electrolysis stops until the group voltage becomes 0 is monitored. g Obtain (step S210).

[0046] In step S210, for each cell group, the voltage drop time t until the group voltage drops to 0 is calculated. g Upon obtaining this, the CPU of the control unit 70 calculates the voltage drop time t for each cell group. g And, reference time t b1 This is compared with the following: Among the cell groups that make up the cell stack 20, the voltage drop time t g is the reference time t b1 Determine whether there are any cell groups shorter than this (step S220). b1 This is a criterion value used to determine whether a cell group contains abnormal cells. Specifically, the reference time t b1 This is the time t, which is expressed by the following equation (1). a This is the time expressed by the following equation (2) using . This reference time t b1 This will be explained in more detail later.

[0047]

number

number

[0048] However, in the above formula (1), V c [cm 3 ] is the volume of the flow path on the hydrogen electrode side in the water electrolysis cell 22, and F w [cm 3 [ / sec] is the amount of associated water per unit time in the water electrolysis cell 22 operating at rated speed. In the above equation (2), tn This is the time from when the water electrolysis operation stops until the voltage of the normal water electrolysis cell 22 becomes 0.

[0049] In step S220, the voltage drop time t g is the reference time t b1 If it is determined that there are no cell groups with a shorter voltage drop time than t (step S220: NO), the CPU of the control unit 70 determines that there are no cell groups containing the abnormal water electrolysis cell 22 (step S230) and terminates this routine. g is the reference time t b1 If it is determined that there is a cell group shorter than (step S220: YES), the CPU of the control unit 70 determines that the cell group contains abnormal cells, estimates the number of abnormal cells in the cell group containing these abnormal cells (hereinafter also referred to as the "abnormal cell group") (step S240), and terminates this routine. When estimating the number of abnormal cells in the abnormal cell group, the time t expressed by equation (1) described above is used with respect to the abnormal cell group. a of and the reference time t g The t in equation (3) below bm Substitute these values ​​to calculate m that satisfies equation (3). Then, estimate that the number of water electrolysis cells 22 in which an anomaly occurs, including at least one of microshorts and pinholes, among the n water electrolysis cells 22 that make up this anomaly cell group, is less than m.

[0050]

number

[0051] However, in equation (3), t n This is the time from when the water electrolysis operation stops until the cell voltage of the normal water electrolysis cell 22 becomes 0. Below, the reference time t b1 This section also describes how the number of abnormal cells in an abnormal cell group is estimated.

[0052] Figure 7 is an explanatory diagram illustrating a linear model of the decrease in cell voltage after the water electrolysis operation is stopped. In Figure 7, the horizontal axis (x axis) represents time from the time the water electrolysis was stopped, and the vertical axis (y axis) represents the cell voltage. In Figure 7, the time from the time the water electrolysis was stopped until the cell voltage became 0 is shown as the voltage drop time t. When the decrease in cell voltage after the water electrolysis was stopped is modeled linearly as in Figure 7, the cell voltage y after time x from the time the water electrolysis was stopped is expressed by the following equation (4).

[0053]

number

[0054] Therefore, in a normal water electrolysis cell 22, the cell voltage y after time x from the cessation of water electrolysis is given by the voltage drop time t, which is the time it takes for the cell voltage of the normal water electrolysis cell 22 to become 0 after the cessation of water electrolysis. n Therefore, it can be expressed by the following equation (5). Also, the cell voltage y in an abnormal cell after time x from the cessation of water electrolysis is given by the voltage drop time t, which is the time it takes for the cell voltage of the abnormal cell to become 0 after the cessation of water electrolysis. f Therefore, it can be expressed by the following equation (6).

[0055]

number

number

[0056] Based on the above, if m water electrolysis cells 22 out of n water electrolysis cells 22 belonging to the same cell group are the abnormal cells described above, then the cell voltage y per water electrolysis cell 22 in this abnormal cell group after time x from the cessation of water electrolysis is expressed by the following equation (7). At this time, the time until the group voltage in this abnormal cell group becomes 0 after the cessation of water electrolysis is the voltage drop time t. bmTherefore, in this abnormal cell group, the cell voltage y per water electrolysis cell 22 after time x from the cessation of water electrolysis can also be expressed by the following equation (8).

[0057]

number

number

[0058] Using equations (7) and (8) described above, the voltage drop time t of this abnormal cell group is calculated. bm Solving for this, we obtain the following equation (9). That is, in a cell group composed of n water electrolysis cells 22, the time until the cell voltage becomes 0 after the water electrolysis stops is the voltage drop time t. f When m abnormal cells occur, the voltage drop time t in the group of abnormal cells is... bm This can be expressed by equation (9). Then, by substituting 1 for m in equation (9), and t f ni t a Substituting this, we obtain equation (2) as described above. That is, in a cell group composed of n water electrolysis cells 22, the time until the cell voltage becomes 0 after the water electrolysis stops is the voltage drop time t. a When one such cell occurs, the voltage drop time t in that cell group is... b1 This can be expressed by equation (2).

[0059]

number

[0060] In step S220 shown in Figure 7, the voltage drop time t for each cell group g And the time t expressed by equation (1) described above... a The reference time t expressed by equation (2) using this formula is t b1 This is a comparison of the time t expressed by equation (1). aThis is the reference value for the voltage drop time used to determine abnormal cells, and this reference time t a This is the upper limit of the voltage drop time of an abnormal cell, used to determine that the water electrolysis cell 22 is an abnormal cell when the reference time is shorter than t. Therefore, if a cell group contains one abnormal cell, the voltage drop time of this abnormal cell is t a Because it becomes shorter than the voltage drop time t of the cell group, g is the reference time t b1 This becomes shorter. Therefore, in step S220, it is necessary to determine whether or not there is an abnormal cell group, that is, This allows us to determine whether or not there is a cell group in which at least one water electrolysis cell 22 is an abnormal cell.

[0061] In step S220, if it is determined that an abnormal cell group exists, the time t represented by the previously described formula (1) is applied to the detected abnormal cell group. a Using this, the t in equation (3) described above bm time t g By substituting these values, we calculate m that satisfies equation (3), and estimate that the number of abnormal cells among the n water electrolysis cells 22 constituting this abnormal cell group that have an abnormality including at least one of a microshort and a pinhole is less than m. Equation (3) is the voltage drop time t of the abnormal cell in equation (9) described above. f ni t a This is the equation obtained by substituting the values. The time t expressed in equation (1) a As previously mentioned, this is the upper limit of the voltage drop time for an abnormal cell, and the actual voltage drop time for an abnormal cell is time t. a This becomes shorter. Therefore, the number of abnormal cells in an abnormal cell group is given by the time t expressed by equation (1). a Using this, the t in equation (3) bm voltage drop time t g It can be estimated that the number is less than the m items calculated by substituting the values.

[0062] With this configuration, the same effects as in the first embodiment can be obtained, and furthermore, since the voltage is detected for each cell group, the configuration related to voltage detection can be simplified compared to the case where the voltage is detected for each water electrolysis cell 22. In addition, when the cell group in which an abnormality has occurred is identified by detecting the voltage for each cell group in this way, it is possible to estimate the number of abnormal cells included in the cell group.

[0063] This disclosure is not limited to the embodiments described above, and can be implemented in various configurations without departing from its spirit. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be replaced or combined as appropriate in order to solve some or all of the above-mentioned problems, or to achieve some or all of the above-mentioned effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of symbols]

[0064] 10…Water electrolysis system 20... Cell stack 22...Water electrolysis cell 30...Power supply 32... Cell monitor 40...Water supply section 41… Pure water tank 42... Anode-side gas-liquid separator 43…Supply pump 44... Circulation pump 50… Supply channel 52…Circulation channel 54... Anode side discharge path 55…Oxygen vent 60... Cathode-side gas-liquid separator 62... Cathode side discharge path 63…Hydrogen emission channel 70... Control Unit 80...Electrolyte membrane 81…Oxygen electrode 82... Hydrogen electrode 83... Anode diffusion layer 84... Cathode diffusion layer 85, 86… Separator 87... Anode side channel 88... Cathode side channel

Claims

1. A water electrolysis system, A water electrolysis cell comprising a solid polymer electrolyte membrane and a pair of electrodes arranged on both sides of the electrolyte membrane, which generates hydrogen and oxygen by the electrolysis of water, A power supply device that applies voltage to the water electrolysis cell, A voltage sensor for detecting the voltage of the water electrolysis cell, Control unit and Equipped with, The control unit, After stopping the water electrolysis operation which involves applying voltage from the power supply to the water electrolysis cell, the voltage of the water electrolysis cell detected by the voltage sensor is acquired. The voltage drop time t is the time from when the electrolysis of water stops until the voltage of the water electrolysis cell becomes zero. ｃ However, the time t shown in equation (1) below ａ When the time is shorter than the specified time, it is determined that an abnormality, including at least one of a microshort and a pinhole, has occurred in the electrolyte membrane. Water electrolysis system. [Math 1] (However, V ｃ F is the volume of the flow path on the hydrogen electrode side in the water electrolysis cell. ｗ This is the amount of associated water per unit time in the water electrolysis cell operating at its rated capacity.

2. A water electrolysis system according to claim 1, The water electrolysis system comprises a cell stack in which a plurality of the water electrolysis cells are stacked, The voltage sensor acquires the voltage of each water electrolysis cell in the cell stack. The control unit determines the occurrence of the abnormality for each individual water electrolysis cell. Water electrolysis system.

3. A water electrolysis system according to claim 1 or 2, The control unit, when a pinhole occurs in the electrolyte membrane, controls the time from when the water electrolysis operation stops until the voltage of the water electrolysis cell becomes 0, which is the time t ａ A predetermined time t that is shorter than ｐ Rather than the voltage drop time t ｃ When the interval is short, it is determined that a pinhole has occurred. Water electrolysis system.

4. A water electrolysis system, A cell stack comprising multiple stacked water electrolysis cells, each comprising a solid polymer electrolyte membrane and a pair of electrodes arranged on both sides of the electrolyte membrane, which generate hydrogen and oxygen by the electrolysis of water, A power supply device that applies voltage to the cell stack, In the cell stack, a voltage sensor is provided to detect the voltage for each cell group composed of n consecutive water electrolysis cells. Control unit and Equipped with, The control unit, After stopping the electrolysis of water operation which involves applying voltage from the power supply to the cell stack, the voltage for each cell group detected by the voltage sensor is acquired. The voltage drop time t from when the operation of the electrolysis of water stops until the voltage of the cell group becomes 0 ｇ is the time t represented by the following formula (1) ａ Using the time t represented by the following formula (2) ｂ１ When there is a cell group shorter than that, in at least one of the water electrolysis cells included in the cell group, at least one of micro shorts and pinholes Even if none of the above are present, it is determined that an anomaly has occurred that includes one of the other. Water electrolysis system. [Math 2] [Math 3] (However, V ｃ F is the volume of the flow path on the hydrogen electrode side in the water electrolysis cell. ｗ t is the amount of associated water per unit time in the water electrolysis cell performing rated operation, ｎ This is the time from when the electrolysis of water is stopped until the voltage of a normal water electrolysis cell becomes zero.

5. A water electrolysis system according to claim 4, The control unit controls the voltage drop time t ｇ that time t ｂ１ When there is a cell group shorter than t, the time t represented by formula (1) is given to that cell group. ａ Using this, the t in equation (3) below ｂｍ at the aforementioned time t ｇ Substitute the values ​​to calculate m that satisfies equation (3), and estimate that the number of water electrolysis cells among the n water electrolysis cells constituting the cell group that have an abnormality including at least one of microshorts and pinholes is less than m. Water electrolysis system. [Math 4] (However, t ｎ This is the time from when the electrolysis of water is stopped until the voltage of a normal water electrolysis cell becomes zero.

6. A method for detecting abnormalities in a water electrolysis system, The application of voltage to a water electrolysis cell comprising a solid polymer electrolyte membrane and a pair of electrodes arranged on both sides of the electrolyte membrane is stopped. After stopping the application of the aforementioned voltage, thereby stopping the operation of water electrolysis involving the generation of hydrogen and oxygen in the water electrolysis cell, the voltage of the water electrolysis cell is detected. The voltage drop time t is the time from when the electrolysis of water stops until the voltage of the water electrolysis cell becomes zero. ｃ However, the time t shown in equation (1) below ａ When the time is shorter than the specified time, it is determined that an abnormality, including at least one of a microshort and a pinhole, has occurred in the electrolyte membrane. Method for detecting abnormalities in a water electrolysis system. [Math 5] (However, V ｃ F is the volume of the flow path on the hydrogen electrode side in the water electrolysis cell. ｗ This is the amount of associated water per unit time in the water electrolysis cell operating at its rated capacity.

7. A method for detecting abnormalities in a water electrolysis system, The voltage application to a cell stack, which consists of multiple stacked water electrolysis cells, each comprising a solid polymer electrolyte membrane and a pair of electrodes positioned on both sides of the electrolyte membrane, is stopped. After stopping the application of the aforementioned voltage, thereby halting the electrolysis of water in the cell stack, which involves the generation of hydrogen and oxygen, the voltage is detected in the cell stack for each cell group composed of n consecutive water electrolysis cells. The voltage drop time t is the time from when the electrolysis of water stops until the voltage of the cell group becomes zero. ｇ However, time t is expressed by the following equation (1) ａ The time t is expressed by the following equation (2) using the following formula. ｂ１ When there are cell groups shorter than [a certain length], it is determined that an abnormality including at least one of a microshort and a pinhole has occurred in at least one of the water electrolysis cells included in the cell group. Method for detecting abnormalities in a water electrolysis system. [Math 6] [Number 7] (However, V ｃ F is the volume of the flow path on the hydrogen electrode side in the water electrolysis cell. ｗ t is the amount of associated water per unit time in the water electrolysis cell performing rated operation, ｎ This is the time from when the electrolysis of water is stopped until the voltage of a normal water electrolysis cell becomes zero.

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