Water electrolysis system

Abstract

A water electrolysis system for generating hydrogen and oxygen by electrolysis of water according to the present invention is provided with: a water electrolysis cell provided with an anode, a cathode, and an electrolyte membrane sandwiched between the anode and the cathode; and a control device for controlling the power supplied to the water electrolysis cells, the control device executing a potential variation process for varying the potential of the anode when the water electrolysis system is started and / or when the water electrolysis system is continuously operated. The potential variation processing includes a potential reduction processing for reducing the potential of the anode to a predetermined potential.

Description

Technical Field

[0001] This disclosure relates to a water electrolysis system. Background Art

[0002] Previously, it was known to produce oxygen and hydrogen by electrolyzing water to generate oxygen at the anode and hydrogen at the cathode, thereby creating a water electrolysis system (Japanese Patent Application Laid-Open No. 2023-128165). This water electrolysis system comprises a stack of multiple water electrolysis chambers, each chamber having a membrane electrode structure in which an ion exchange membrane is sandwiched between the anode and cathode. The anode and cathode each have a catalyst layer and a power supply element.

[0003] During startup and continuous operation of a water electrolysis system, the chambers can sometimes become poisoned due to the water flowing through the system and impurities generated within it. This can lead to reduced catalyst activity and deterioration of the electrolyte membrane (ion exchange membrane). In cases of chamber poisoning, there are concerns about reduced oxygen and hydrogen production and decreased production efficiency. Summary of the Invention

[0004] This disclosure can be implemented in the following ways.

[0005] (1) A water electrolysis system is provided according to one aspect of the present disclosure.

[0006] A water electrolysis system for generating hydrogen and oxygen by electrolyzing water comprises: a water electrolysis chamber having an anode, a cathode, and an electrolyte membrane sandwiched between the anode and the cathode; and a control device for controlling the power supplied to the water electrolysis chamber, wherein the control device performs a potential variation process that causes the potential of the anode to vary during at least one of the start-up and continuous operation of the water electrolysis system, the potential variation process including a potential reduction process that causes the potential of the anode to decrease towards a predetermined potential.

[0007] According to this method, in at least one of the following scenarios—during startup or continuous operation of a water electrolysis system where there is a concern about poisoning in the water electrolysis chamber—the control device can restore the electrolysis performance of the water electrolysis chamber by performing a potential change process. Thus, in the water electrolysis system, the reduction in the amount and efficiency of oxygen and hydrogen production can be suppressed.

[0008] (2) It can also be configured such that, based on the above method, the control device performs the above potential change processing once or more but less than 30 times.

[0009] According to this method, the control device can restore the electrolysis performance of the water electrolysis chamber by performing a potential change process more than once and less than 30 times.

[0010] (3) It can also be configured such that, based on the above method, after the control device stops the supply of the above power to the above water electrolysis chamber, the hydrogen generated in the above cathode passes through the above electrolyte membrane and moves from the above cathode to the above anode, thereby performing the above potential reduction process.

[0011] According to this method, after the control device stops supplying power to the water electrolysis chamber, it causes the hydrogen generated at the cathode to pass through the electrolyte membrane and move from the cathode to the anode, thereby enabling the potential reduction process to be performed.

[0012] (4) It can also be configured such that, based on the above method, the control device performs the above potential change processing by controlling at least one of the current value and voltage value when the power is supplied to the water electrolysis chamber.

[0013] According to this method, the control device can perform potential variation processing by controlling at least one of the current value and voltage value when power is supplied to the water electrolysis chamber.

[0014] (5) It can also be configured such that, based on the above method, the thickness of the electrolyte membrane is less than 25 μm.

[0015] According to this method, when the thickness of the electrolyte membrane is less than 25 μm, the control device can restore the electrolysis performance of the water electrolysis chamber.

[0016] This disclosure can be implemented in various ways other than the water electrolysis system described above. For example, it can be implemented by a method for manufacturing a water electrolysis system, a water electrolysis method using the water electrolysis system, a control method for the water electrolysis system, a computer program for implementing the control method, and a non-transitory recording medium containing the computer program.

[0017] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, in which the same reference numerals denote the same elements. Attached Figure Description

[0018] Figure 1 It is a diagram showing the structure of a water electrolysis system.

[0019] Figure 2 This is a cross-sectional schematic diagram showing the structure of the water electrolysis chamber.

[0020] Figure 3 This is a diagram used to illustrate the details of handling potential changes.

[0021] Figure 4 This is a table representing the research results of various conditions in the potential variation treatment.

[0022] Figure 5It is a graph representing the change in current density according to the number of times the potential change processing is executed.

[0023] Figure 6 This is a graph showing the relationship between the thickness of the electrolyte membrane and the time required for the potential reduction treatment. DETAILED DESCRIPTION

[0024] A. Implementation Method 1:

[0025] Figure 1 This is a diagram showing the structure of a water electrolysis system 1. The water electrolysis system 1 generates hydrogen and oxygen through the electrolysis of water. The water electrolysis system 1 includes a stack of multiple water electrolysis chambers 22, a power supply 30, a chamber monitor 32, a water supply unit 40, an oxygen discharge unit 50, a hydrogen discharge unit 60, and a control device 70.

[0026] Figure 2 This is a cross-sectional schematic diagram showing the structure of the water electrolysis chamber 22. The water electrolysis chamber 22 includes an electrolyte membrane 80, an anode 81, a cathode 82, an anode-side diaphragm 85, a cathode-side diaphragm 86, an anode-side flow path 87, and a cathode-side flow path 88.

[0027] The electrolyte membrane 80 is sandwiched between an anode 81 and a cathode 82. The electrolyte membrane 80 is a membrane composed of a polymer having ion-exchange groups. For example, the electrolyte membrane 80 may also have at least one of sulfonic acid groups, phosphate groups, and quaternary ammonium groups as ion-exchange groups. The electrolyte membrane 80 can be an anion-exchange membrane or a cation-exchange membrane. For example, the electrolyte membrane 80 may be a membrane composed of a perfluorocarbon sulfonic acid polymer, or a membrane composed of a polymer with either polyether ether ketone or polybenzimidazole as the main component. Metals such as iridium, platinum, cerium, and manganese, or cations, may also be incorporated into the electrolyte membrane 80. When metals are incorporated into the electrolyte membrane 80, the amount of metal contained in the electrolyte membrane 80 may be 5 μg / cm³. 2 The following values ​​can also be 3 μg / cm 2 The electrolyte membrane 80 may contain a metal, an oxide, or an ionic state. In this embodiment, the electrolyte membrane 80 is a proton (hydrogen ion) exchange membrane.

[0028] The anode 81 has an anode catalyst layer 811 and an anode gas diffusion layer 812. The anode catalyst layer 811 is stacked on one side of the electrolyte membrane 80. The anode gas diffusion layer 812 is stacked in the stacking direction D of the water electrolysis chamber 22 on the side of the anode catalyst layer 811 opposite to the side opposite to the electrolyte membrane 80.

[0029] The anode catalyst layer 811 is a layer that functions as an anode electrode for oxygen generation. For example, the anode catalyst layer 811 is formed by supporting the anode catalyst on a carrier using an adhesive.

[0030] An anode catalyst is a metal particle that catalyzes the reaction that generates oxygen. An anode catalyst may contain at least one of the following metals: platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. An anode catalyst may also contain two or more of the above metals. Preferably, the anode catalyst is primarily composed of either iridium or ruthenium. The anode catalyst may also be an oxide, nitride, sulfide, or phosphide. Preferably, the anode catalyst is either an oxide or a nitride. The anode catalyst may also be composed of at least one of iridium particles, iridium alloy particles, or composite particles containing iridium. For example, iridium alloy particles and iridium-containing composite particles contain at least one metal other than iridium from the following metals: ruthenium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. Iridium alloy particles and iridium-containing composite particles may also contain two or more of the aforementioned metals. The ratio of elements other than iridium in the iridium alloy particles is not particularly limited; for example, it may be 0.11 atm% or more, or 60 atm% or less. The particle size of the metal particles constituting the anode catalyst is not particularly limited; for example, it may be 1 nm or more, or 5000 nm or less. In this disclosure, the particle size of the metal particles is the average crystallite diameter determined by X-ray diffraction. Furthermore, in another embodiment, the particle size of the metal particles may also be the average particle size calculated by measuring the particle size of a predetermined number of metal particles separately using an electron microscope and averaging the measured particle sizes of each metal particle. To calculate the average particle size, for example, the particle size of a metal particle ranging from 100 to 1000 is determined using an electron microscope.

[0031] The anode catalyst can also be supported on a carrier. The method for supporting the anode catalyst on the carrier is not particularly limited; for example, known methods such as impregnation support can be used. The carrier for supporting the anode catalyst can be primary particles or secondary particles. The particle size of the primary particles constituting the carrier can be, for example, 5 nm or more, or 5000 nm or less. The loading ratio of the anode catalyst supported on the carrier is not particularly limited; for example, it can be 1% or more, 50% or more, or 100% or less. The carrier for supporting the anode catalyst is, for example, composed of oxides. The oxide constituting the carrier is, for example, at least one of titanium oxide, niobium oxide, tin oxide, tungsten oxide, and molybdenum oxide. The carrier for supporting the anode catalyst can also be composed of a mixture containing at least one of the above oxides.

[0032] The binder used when supporting the anode catalyst on the support is, for example, composed of at least one of a polymer having ion-exchange groups and an ionomer. The binder used when supporting the anode catalyst on the support may also have at least one of sulfonic acid groups, phosphate groups, and quaternary ammonium groups as ion-exchange groups. The binder used when supporting the anode catalyst on the support may be composed of anion-exchange polymers or cation-exchange polymers. The binder used when supporting the anode catalyst on the support may also be composed of perfluorocarbon sulfonic acid polymers. The binder may also be composed of polymers with either polyetheretherketone or polybenzimidazole as the main component.

[0033] The anode gas diffusion layer 812 is a layer used for distributing gas. The anode gas diffusion layer 812 is composed of at least one of, for example, carbon paper, carbon fiber, carbon cloth, porous titanium, and titanium fiber. The anode gas diffusion layer 812 may also be a structure combining two or more of the above materials. The anode gas diffusion layer 812 may also have a microporous layer composed of at least one of carbon and titanium particles.

[0034] The cathode 82 has a cathode catalyst layer 821 and a cathode gas diffusion layer 822. The cathode catalyst layer 821 is stacked on the other side of the electrolyte membrane 80. The cathode gas diffusion layer 822 is stacked in the stacking direction D of the water electrolysis chamber 22 on the side of the cathode catalyst layer 821 opposite to the side opposite to the electrolyte membrane 80.

[0035] The cathode catalyst layer 821 is a layer that functions as a cathode electrode for hydrogen production. For example, the cathode catalyst is supported on a carrier using a binder, thereby forming the cathode catalyst layer 821.

[0036] A cathode catalyst is a metal particle that catalyzes the reaction to produce hydrogen. A cathode catalyst may contain at least one of the following metals: platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. A cathode catalyst may also contain two or more of the aforementioned metals. A cathode catalyst may also be an oxide, nitride, sulfide, or phosphide. A cathode catalyst may also be composed of any one of platinum particles, platinum alloy particles, or platinum-containing composite particles. Platinum alloy particles and platinum-containing composite particles may contain at least one of the following metals as a metal other than platinum: ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, lanthanum, cerium, praseodymium, neodymium, samarium, gadolinium, and yttrium. Platinum alloy particles and platinum-containing composite particles may also contain two or more of the aforementioned metals. The percentage of elements other than platinum in the platinum alloy particles is not particularly limited; for example, it may be 0.11 atm% or more, or 60 atm% or less. The particle size of the metal particles constituting the cathode catalyst is not particularly limited; for example, it may be 1 nm or more, or 100 nm or less.

[0037] The cathode catalyst can also be supported on a support. The method of supporting the cathode catalyst on the support is not particularly limited; for example, known methods such as impregnation support can be used. The support for the cathode catalyst can be primary particles or secondary particles. The particle size of the primary particles constituting the support can be, for example, 5 nm or more, or 5000 nm or less. The loading ratio of the cathode catalyst supported on the support is not particularly limited; for example, it can be 1% or more, 18% or more, 48% or less, or 70% or less. The support for the cathode catalyst is, for example, composed of at least one of conductive carbon, oxides, or mixtures containing carbon and oxides. The carbon constituting the support may be at least one of the following: acetylene black, Ketjen black, and other carbon blacks such as furnace black, activated carbon, lead black, glassy carbon, graphite, graphene, carbon fiber, carbon nanotubes, carbon nitride, carbon sulfide, carbon phosphide, channel black, roller black, disk black, oil furnace black, gas furnace black, lampblack, pyrolysis black, and vulcan black. The support for the cathode catalyst may also be composed of a mixture containing at least one of the above-mentioned carbons. The oxide constituting the support may be at least one of titanium oxide, niobium oxide, tin oxide, tungsten oxide, and molybdenum oxide. The support for the cathode catalyst may also be composed of a mixture containing at least one of the above-mentioned oxides.

[0038] The binder used when supporting the cathode catalyst on the support is, for example, composed of at least one of a polymer having ion-exchange groups and an ionomer. The binder used when supporting the cathode catalyst on the support may also have at least one of sulfonic acid groups, phosphate groups, and quaternary ammonium groups as ion-exchange groups. The binder used when supporting the cathode catalyst on the support may be composed of anion-exchange polymers or cation-exchange polymers. The binder used when supporting the cathode catalyst on the support may also be composed of perfluorocarbon sulfonic acid polymers. The binder may also be composed of polymers with either polyetheretherketone or polybenzimidazole as the main component.

[0039] The cathode gas diffusion layer 822 is a layer used for distributing gas. The cathode gas diffusion layer 822 is composed of at least one of, for example, carbon paper, carbon fiber, carbon cloth, porous titanium, and titanium fiber. The cathode gas diffusion layer 822 may also be a structure combining two or more of the above materials. The cathode gas diffusion layer 822 may also have a microporous layer composed of at least one of carbon and titanium particles.

[0040] Two diaphragms 85 and 86 are disposed at both ends of the stacking direction D of the water electrolysis chamber 22. The anode-side diaphragm 85 is opposite to the anode gas diffusion layer 812. The cathode-side diaphragm 86 is opposite to the cathode gas diffusion layer 822.

[0041] The anode-side flow path 87 extends from the anode-side diaphragm 85 through the anode 81 along the stacking direction D of the water electrolysis chamber 22. The cathode-side flow path 88 extends from the cathode-side diaphragm 86 through the cathode 82 along the stacking direction D of the water electrolysis chamber 22.

[0042] like Figure 1 As shown, power supply 30 supplies power to water electrolysis chamber 22. Chamber monitor 32 monitors the status of water electrolysis chamber 22.

[0043] like Figure 1 and Figure 2As shown, the water supply unit 40 supplies water to the water electrolysis chamber 22. In this embodiment, the water supply unit 40 supplies water to the anode 81 of the water electrolysis chamber 22. The water supply unit 40 includes a tank 41, a supply flow path 43, a circulation flow path 45, a supply pump 47, and a circulation pump 49. The tank 41 stores the water supplied to the water electrolysis chamber 22. The supply flow path 43 connects the tank 41 to the anode-side gas-liquid separator 53 (described later). The circulation flow path 45 connects the anode-side gas-liquid separator 53 to the anode-side flow path 87. The supply pump 47 is provided in the supply flow path 43 to supply water from the tank 41 to the anode-side gas-liquid separator 53. The circulation pump 49 is provided in the circulation flow path 45 to supply water from the anode-side gas-liquid separator 53 to the anode-side flow path 87. Furthermore, in other embodiments, the water supply unit 40 may supply water to the cathode 82 instead of the anode 81, or supply water to both simultaneously.

[0044] The oxygen discharge unit 50 includes an anode-side discharge path 51, an anode-side gas-liquid separator 53, and an oxygen discharge path 55. The anode-side discharge path 51 connects the anode-side gas-liquid separator 53 to an anode-side flow path 87. The anode-side gas-liquid separator 53 separates the fluid discharged from the anode-side flow path 87 into oxygen and water. The oxygen discharge path 55 discharges the oxygen separated in the anode-side gas-liquid separator 53 to the outside. The oxygen discharge path 55 may be connected, for example, to a tank (not shown) for storing oxygen.

[0045] The hydrogen discharge unit 60 includes a cathode-side discharge path 61, a cathode-side gas-liquid separator 63, and a hydrogen discharge path 65. The cathode-side discharge path 61 connects the cathode-side gas-liquid separator 63 to a cathode-side flow path 88. The cathode-side gas-liquid separator 63 separates the fluid discharged from the cathode-side flow path 88 into hydrogen and water. The hydrogen discharge path 65 discharges the hydrogen separated in the cathode-side gas-liquid separator 63 to the outside. The hydrogen discharge path 65 may be connected, for example, to a tank (not shown) for storing hydrogen.

[0046] During the electrolytic treatment of water electrolysis, water is supplied from tank 41 to anode 81, and electricity is supplied from power source 30 to water electrolysis chamber 22. This electrolyzes the water supplied to anode 81 to generate hydrogen ions and oxygen. The oxygen generated at anode 81, along with a portion of the water remaining after electrolysis, is conveyed through anode-side flow path 87 and anode-side discharge path 51 to anode-side gas-liquid separator 53. The oxygen separated in anode-side gas-liquid separator 53 is discharged to the outside via oxygen discharge path 55. The water separated in anode-side gas-liquid separator 53, along with the water supplied from tank 41, is supplied back to anode 81 through circulation flow path 45. The hydrogen ions generated at anode 81, along with a portion of the water remaining after electrolysis, move through electrolyte membrane 80 towards cathode 82. At cathode 82, hydrogen is generated by the combination of hydrogen ions and electrons. The hydrogen generated at cathode 82, along with water that moves from anode 81 to cathode 82 via the electrolyte membrane 80 accompanied by hydrogen ions, is conveyed to cathode-side gas-liquid separator 63 via cathode-side flow path 88 and cathode-side discharge path 61. The hydrogen separated in cathode-side gas-liquid separator 63 is discharged to the outside via hydrogen discharge path 65.

[0047] Control device 70 controls water electrolysis system 1. During electrolysis, control device 70 controls the operation of supply pump 47 and circulation pump 49. This allows control device 70 to supply water to anode 81 at the desired flow rate. Additionally, during electrolysis, control device 70 sets current and voltage values ​​to operate power supply 30 such that anode 81 and cathode 82 are at predetermined electrolysis potentials. This allows control device 70 to control the power supplied to water electrolysis chamber 22. The electrolysis potential is arbitrary. The electrolysis potential of anode 81 is, for example, 1.5V or higher. During startup or continuous operation of water electrolysis system 1, control device 70 performs at least one potential change operation to restore the electrolysis performance of water electrolysis chamber 22.

[0048] Figure 3 This is a diagram used to illustrate the details of PF in handling potential changes. Figure 3 The vertical axis of each graph represents the potential of anode 81. Figure 3The horizontal axis of each graph represents time. The first potential P1 can be equal to, higher than, or lower than the electrolysis potential P3. The first potential P1 is preferably 1.0V (vsRHE) or higher, more preferably 1.4V (vsRHE) or higher. The first potential P1 is preferably 3.0V (vsRHE) or lower, more preferably 2.0V (vsRHE) or lower. The second potential P2 is lower than both the first potential P1 and the electrolysis potential P3. The second potential P2 can be equal to or higher than the natural potential P4. The second potential P2 is preferably -0.5V (vsRHE) or higher, more preferably 0.0V (vsRHE) or higher. The second potential P2 is preferably 1.0V (vsRHE) or lower, more preferably 0.7V (vsRHE) or lower, and even more preferably 0.2V (vsRHE) or lower.

[0049] The potential variation process PF is a process that changes the potential of the anode 81. The potential variation process PF includes a potential reduction process PD that lowers the potential of the anode 81 to a predetermined second potential P2. The potential variation process PF may also include a potential increase process PU that raises the potential of the anode 81 to a predetermined first potential P1.

[0050] When the water electrolysis system 1 is started, the control device 70 performs a potential change process PF before starting the electrolysis treatment PE. The water electrolysis system 1 is started when the power supply 30 is turned on and the control device 70 is activated. At the start of the water electrolysis system 1, the potential of the anode 81 is the natural potential P4. Therefore, when the potential change process PF is performed once at the start of the water electrolysis system 1, the control device 70 performs the following process. In this case, the control device 70 sequentially performs a potential rise process PU, which raises the potential of the anode 81 from the natural potential P4 to the first potential P1, and a potential decrease process PD, which lowers the potential of the anode 81 from the first potential P1 to the second potential P2. When the potential change process PF is performed N times (N is an integer greater than or equal to 2) at the start of the water electrolysis system 1, the control device 70 performs the following process. In this case, during the first potential change process PF, the control device 70 sequentially executes a potential rise process PU, which raises the potential of the anode 81 from the natural potential P4 to the first potential P1, and a potential decrease process PD, which lowers the potential of the anode 81 from the first potential P1 to the second potential P2. In subsequent potential change processes PF, the control device 70 sequentially executes N-1 times the potential rise process PU, which raises the potential of the anode 81 from the second potential P2 to the first potential P1, and the potential decrease process PD, which lowers the potential of the anode 81 from the first potential P1 to the second potential P2. After the potential change process PF ends, the control device 70 initiates the electrolysis process PE by changing the potential of the anode 81 from the second potential P2 to the electrolysis potential P3.

[0051] During continuous operation of the water electrolysis system 1, the control device 70 performs a potential change process PF before restarting the electrolysis process PE. Continuous operation of the water electrolysis system 1 means continuously performing the electrolysis process PE for a predetermined time or longer. For example, the predetermined time is calculated based on the time required from the start of the electrolysis process PE until the current density, calculated using data output from the small chamber monitor 32, becomes less than a predetermined threshold. During continuous operation of the water electrolysis system 1, the potential of the anode 81 is the electrolysis potential P3. Therefore, when the potential change process PF is performed once during continuous operation of the water electrolysis system 1, the control device 70 performs the following process. In this case, the control device 70 does not perform a potential rise process PU, but performs a potential decrease process PD that lowers the potential of the anode 81 from the electrolysis potential P3 to the second potential P2. When the potential change process PF is performed N times during continuous operation of the water electrolysis system 1, the control device 70 performs the following process. In this case, during the first potential change process PF, the control device 70 does not execute the potential rise process PU, but instead executes the potential decrease process PD, which lowers the potential of the anode 81 from the electrolysis potential P3 to the second potential P2. In subsequent potential change processes PF, the control device 70 sequentially executes N-1 times each of the potential rise process PU (raising the potential of the anode 81 from the second potential P2 to the first potential P1) and the potential decrease process PD (lowering the potential of the anode 81 from the first potential P1 to the second potential P2). After the potential change process PF ends, the control device 70 restarts the electrolysis process PE by changing the potential of the anode 81 from the second potential P2 to the electrolysis potential P3. Furthermore, when the potential change process PF executed during continuous operation of the water electrolysis system 1 ends, the control device 70 can also stop the water electrolysis system 1 to end the electrolysis process PE.

[0052] like Figure 2 As shown, for example, after stopping the power supply to the water electrolysis chamber 22, the control device 70 causes the hydrogen generated at the cathode 82 to permeate through the electrolyte membrane 80 and move from the cathode 82 to the anode 81. Thus, the control device 70 performs a potential reduction process PD. That is, the control device 70 does not supply power from the power source 30 to the water electrolysis chamber 22, but utilizes the hydrogen permeation characteristics of the hydrogen generated at the cathode 82 permeating through the electrolyte membrane 80 to reduce the potential of the anode 81 to a second potential P2. The hydrogen permeation characteristics of the electrolyte membrane 80 are also called hydrogen cross-leakage.

[0053] Furthermore, the control device 70 can also supply power from the power source 30 to the water electrolysis chamber 22 by controlling at least one of the current value and voltage value when supplying power to the water electrolysis chamber 22, and perform a potential reduction process PD. When performing the potential reduction process PD by controlling the current value when supplying power to the water electrolysis chamber 22, the control device 70 performs the following process. In this case, the control device 70, for example, sets a current value smaller than the current value set when the potential of the anode 81 is formed to either the first potential P1 or the electrolysis potential P3, to operate the power source 30. When performing the potential reduction process PD by controlling the voltage value when supplying power to the water electrolysis chamber 22, the control device 70 performs the following process. In this case, the control device 70, for example, sets a voltage value smaller than the voltage value set when the potential of the anode 81 is formed to either the first potential P1 or the electrolysis potential P3, to operate the power source 30.

[0054] The control device 70 supplies power from the power source 30 to the water electrolysis chamber 22 by controlling at least one of the current value and voltage value when supplying power to the water electrolysis chamber 22, and performs a potential rise process PU. When performing the potential rise process PU by controlling the current value when supplying power to the water electrolysis chamber 22, the control device 70 performs the following process: In this case, the control device 70, for example, sets a current value larger than the current value set when the potential of the anode 81 is formed to the second potential P2, to operate the power source 30. When performing the potential rise process PU by controlling the voltage value when supplying power to the water electrolysis chamber 22, the control device 70 performs the following process: In this case, the control device 70, for example, sets a voltage value larger than the voltage value set when the potential of the anode 81 is formed to the second potential P2, to operate the power source 30. Furthermore, during the execution of the potential rise process PU, power is supplied from the power source 30 to the water electrolysis chamber 22. Therefore, during the execution of the potential rise process PU, the potential change of anode 81 caused by the power supply is larger than the potential change of anode 81 caused by hydrogen cross-leakage. Thus, during the execution of the potential rise process PU, the potential change of anode 81 caused by hydrogen cross-leakage can be substantially ignored.

[0055] In the potential variation processing PF, the potential of the anode 81 can be detected, for example, using at least one of a cell with a reference electrode and a bipolar cell. Furthermore, when the potential of the anode 81 decreases due to hydrogen cross-leakage, the potential difference between the anode 81 and the cathode 82 decreases. When the potential of the anode 81 increases due to power supply, the potential difference between the anode 81 and the cathode 82 increases. The potential difference is equal to the voltage. Therefore, in the potential variation processing PF, the control device 70 uses the output of the cell monitor 32 to confirm the voltage shift of each of the plurality of water electrolysis cells 22 constituting the cell stack 20, thereby confirming the progress of the potential variation processing PF.

[0056] Figure 4 This is a table showing the results of research on various conditions in the potential variation treatment of PF. Figure 4 The diagram shows the evaluation results of various conditions and the number of times the potential variation treatment PF was performed during the startup of the water electrolysis system 1 for each of the multiple water electrolysis chambers 22 with electrolyte membranes 80 having different thicknesses and cerium contents.

[0057] The water electrolysis chamber 22 in Examples 1 to 11 and the Reference Example was manufactured as follows. An anode catalyst layer 811 was formed by dispersing, mixing, and coating an anode catalyst onto a support. ElystIr75 manufactured by Umicore was used as the anode catalyst. A cathode catalyst layer 821 was formed by dispersing, mixing, and coating a cathode catalyst onto a support. Platinum-supported carbon was used as the cathode catalyst. The platinum loading in the platinum-supported carbon used as the cathode catalyst was 10 wt% to 50 wt%. A perfluorocarbon sulfonate polymer based on Nafion (registered trademark) manufactured by Chemours was used as the binder for each catalyst layer. The equivalent weight (EW) of the perfluorocarbon sulfonate polymer used as the binder was 1100. An electrolyte membrane 80 was sandwiched between the anode catalyst layer 811 and the cathode catalyst layer 821, and a pressure of 3 MPa was applied at a temperature of 145°C to heat-press the anode catalyst layer 811, the electrolyte membrane 80, and the cathode catalyst layer 821 together. Thus, a membrane electrode assembly Q was fabricated. As the electrolyte membrane 80, a perfluorocarbon sulfonate polymer with varying thicknesses and cerium contents was used. An anode gas diffusion layer 812, composed of a porous metal structure, was bonded to the anode 81 side of the membrane electrode assembly Q, and a cathode gas diffusion layer 822, composed of carbon fibers, was bonded to the cathode 82 side of the membrane electrode assembly Q. Thus, a membrane electrode gas diffusion layer assembly R was fabricated. GDL22BB carbon fiber manufactured by SGL Corporation was used. The fabricated membrane electrode gas diffusion layer assembly R has a dimension of 1 cm. 2Furthermore, the water electrolysis chamber 22 can use any material and composition for the electrolyte membrane 80, anode catalyst layer 811, anode gas diffusion layer 812, cathode catalyst layer 821, and cathode gas diffusion layer 822. Additionally, the temperature and pressure during the hot-pressing of the anode catalyst layer 811, electrolyte membrane 80, and cathode catalyst layer 821 are not particularly limited, and any temperature and pressure can be appropriately set.

[0058] The conditions in the potential change treatment PF are set as follows: The temperature of the water electrolysis chamber 22 is set to 50°C. The second potential P2 is set to the natural potential P4 of the anode 81. The natural potential P4 of the anode 81 is below 0.1V. The electrolysis potential P3 is set to 1.8V. The potential rise treatment PU is performed by controlling at least one of the current value and voltage value when power is supplied to the water electrolysis chamber 22. The required time for the potential rise treatment PU is set to 3 minutes. The potential decrease treatment PD is performed by utilizing the hydrogen permeation characteristics of the electrolyte membrane 80 without supplying power to the water electrolysis chamber 22.

[0059] The various conditions in the potential variation treatment PF are evaluated as follows. The hydrogen permeation characteristics of the electrolyte membrane 80, the time required for the potential reduction treatment PD, and the current / voltage characteristics are evaluated under the condition that ultrapure water flows to the anode 81. The total time required for the potential variation treatment PF is calculated by multiplying the total time required for the potential rise treatment PU and the time required for the potential reduction treatment PD by the number of times the potential variation treatment PF is performed. The longer the total time required for the potential variation treatment PF, the later the timing for starting the electrolytic treatment of PE is delayed. Therefore, the shorter the total time required for the potential variation treatment PF, the better, within the range that can restore the electrolytic performance of the water electrolysis chamber 22. Therefore, for the total time required for the potential variation treatment PF, a shorter time "A" is the highest evaluation, and a longer time "C" is the lowest evaluation.

[0060] The water electrolysis chamber 22 was evaluated as follows. The performance of the water electrolysis chamber 22 was evaluated under atmospheric pressure without applying gas pressure to the anode 81 or cathode 82. In Examples 1 to 11, the water electrolysis chamber 22 was evaluated by measuring the current density when performing electrolysis treatment PE with the electrolysis potential P3 controlled at 1.8V after the potential change treatment PF was completed. In the reference example, the water electrolysis chamber 22 was evaluated by measuring the current density when performing electrolysis treatment PE with the electrolysis potential P3 controlled at 1.8V without performing the potential change treatment PF after the start-up of the water electrolysis system 1. The higher the electrolysis performance of the water electrolysis chamber 22, the greater the current density when performing electrolysis treatment PE. The lower the electrolysis performance of the water electrolysis chamber 22, the smaller the current density when performing electrolysis treatment PE. Therefore, for the effect of the potential change treatment PF, "A" with a larger current density when performing electrolysis treatment PE is the highest evaluation, and "C" with a smaller current density when performing electrolysis treatment PE is the lowest evaluation. In each of the water electrolysis chambers 22 of Examples 1 to 11, where the electrolysis of PE was performed after the potential variation treatment (PF), the maximum value of the saturation current density when the electrolysis of PE was performed with the electrolysis potential P3 controlled at 1.8V was 3.0 A / cm². 2 In the water electrolysis chamber 22 of the reference example where electrolysis of PE is performed without performing potential change treatment PF, the current density when electrolyzing PE is performed with the electrolysis potential P3 controlled at 1.8V is less than 2.5A / cm². 2 Therefore, the effect of the potential variation treatment PF was evaluated based on the saturation current density. Furthermore, in the electrolytic treatment of PE, while controlling the current supplied to the water electrolysis chamber 22, the water electrolysis chamber 22 can also be evaluated, for example, using the saturation voltage during the electrolytic treatment of PE.

[0061] In Examples 1 to 11, where the electrolysis treatment PE is performed after the potential change treatment PF, the current density during the electrolysis treatment PE is higher than in the reference example where the electrolysis treatment PE is performed without the potential change treatment PF. Therefore, the control device 70 can restore the electrolysis performance of the water electrolysis chamber 22 by performing the potential change treatment PF at least once.

[0062] Figure 5 It is a graph representing the change in current density according to the number of times the power factor (PF) is processed based on potential changes. Figure 5 The vertical axis represents the current density when electrolytic treatment of PE is performed with the electrolysis potential P3 controlled at 1.8V. Figure 5 The horizontal axis represents the elapsed time from the start of the electrolytic treatment of PE. The current density during the electrolytic treatment of PE is equal when the potential variation treatment of PF is performed 6 times, 18 times, and 30 times. Additionally, as... Figure 4 As shown in Examples 1-3, 9, and 10, the current density during the electrolysis treatment of PE is the same whether the potential variation treatment PF is performed once, twice, six times, 18 times, or 30 times. Therefore, the control device 70 performs the potential variation treatment PF for example, more than once and less than 30 times. Here, if it is possible to obtain the same effect as restoring the electrolysis performance of the water electrolysis chamber 22, the shorter the total time required for the potential variation treatment PF, the better. Figure 4 As shown in Examples 1 to 3, when the thickness of the electrolyte membrane 80 and the cerium content are equal, the fewer times the potential change process PF is executed, the shorter the total time required for the potential change process PF. Therefore, the control device 70 preferably executes the potential change process PF 1 to 18 times, more preferably 1 to 6 times. Furthermore, the number of times the potential change process PF is executed is not limited to the above. The control device 70 may also execute the potential change process PF 31 times or more.

[0063] like Figure 4 As shown in Examples 1 to 3, the current density during the electrolysis of PE is the same when the total time required for the potential variation treatment PF is 30 minutes, 90 minutes, and 150 minutes. Therefore, the control device 70 performs the potential variation treatment PF, for example, with the total time required for the potential variation treatment PF being less than 150 minutes. Here, if it is possible to obtain the same effect of restoring the electrolysis performance of the water electrolysis chamber 22, the shorter the total time required for the potential variation treatment PF, the better. Therefore, the control device 70 preferably performs the potential variation treatment PF with a total time required for the potential variation treatment PF being less than 90 minutes, and more preferably with a total time required for the potential variation treatment PF being less than 30 minutes.

[0064] Figure 6 This is a graph showing the relationship between the thickness of the electrolyte membrane 80 and the time required for the potential reduction treatment of the PD. The greater the thickness of the electrolyte membrane 80, the more difficult it is for hydrogen generated at the cathode 82 to permeate through the electrolyte membrane 80, and the less hydrogen may move from the cathode 82 to the anode 81 per unit time. The less hydrogen moves from the cathode 82 to the anode 81 per unit time, the longer the time required for the potential reduction treatment of the PD. In fact, in Example 11, where the thickness of the electrolyte membrane 80 is 50 μm, the time required for the potential reduction treatment of the PD is longer compared to Examples 1-10 where the thickness of the electrolyte membrane 80 is 25 μm or less. The longer the time required for the potential reduction treatment of the PD, the longer the total time required for the potential variation treatment of the PF. Furthermore, as... Figure 4As shown, in Example 11 where the thickness of the electrolyte membrane 80 is 50 μm, the current density during PE electrolysis is lower compared to Examples 1-10 where the thickness of the electrolyte membrane 80 is 25 μm or less. Therefore, when the control device 70 utilizes the hydrogen permeation characteristics of the electrolyte membrane 80 to perform the potential reduction treatment (PD), a thickness of 25 μm or less for the electrolyte membrane 80 is preferable. Here, in Examples 2 where the thickness of the electrolyte membrane 80 is 15 μm and in Example 8 where the thickness of the electrolyte membrane 80 is 25 μm, the current density during PE electrolysis is equal, and the same effect of restoring the electrolysis performance of the water electrolysis chamber 22 can be obtained. Therefore, when the control device 70 utilizes the hydrogen permeation characteristics of the electrolyte membrane 80 to perform the potential reduction treatment (PD), a thickness of 15 μm or less for the electrolyte membrane 80 is more preferable. Furthermore, in Example 4 where the thickness of the electrolyte membrane 80 is 8 μm, the time required for the potential reduction treatment (PD) is shorter compared to Example 1 where the thickness of the electrolyte membrane 80 is 15 μm. The shorter the time required for the potential reduction treatment (PD), the shorter the total time required for the potential variation treatment (PF). Therefore, when the control device 70 utilizes the hydrogen permeation characteristics of the electrolyte membrane 80 to perform the potential reduction treatment (PD), it is further preferable that the thickness of the electrolyte membrane 80 is 8 μm or less. Furthermore, the thickness of the electrolyte membrane 80 is not limited to the above. The thickness of the electrolyte membrane 80 can be greater than 25 μm or greater than 50 μm. The thickness of the electrolyte membrane 80 can be measured, for example, by at least one of SEM (Scanning Electron Microscope) measurement and microscopic measurement.

[0065] By incorporating cerium into the electrolyte membrane 80, the durability of the electrolyte membrane 80 can be improved. However, cerium is a cation, so the higher the cerium content of the electrolyte membrane 80, the more difficult it is for hydrogen generated at the cathode 82 to permeate through the electrolyte membrane 80. Therefore, the amount of hydrogen moving from the cathode 82 to the anode 81 per unit time may decrease. In fact, the cerium content of the electrolyte membrane 80 is 5 μg / cm³. 2 In Example 2, the cerium content of the electrolyte membrane 80 was 0 μg / cm³. 2 Compared to Example 7, the time required for potential reduction treatment of PD is longer. The cerium content in the electrolyte membrane 80 is 3 μg / cm³. 2 In Example 5, the cerium content of the electrolyte membrane 80 was 0 μg / cm³. 2Compared to Example 4, the time required for the potential reduction treatment of PD is longer. In Examples 4 and 5, where the thickness of the electrolyte membrane 80 is 8 μm, the increase in the time required for the potential reduction treatment of PD due to the presence of cerium in the electrolyte membrane 80 is greater than that in Examples 2 and 7, where the thickness of the electrolyte membrane 80 is 15 μm. Therefore, the cerium content of the electrolyte membrane 80 can be determined based on the thickness of the electrolyte membrane 80 to make the time required for the potential reduction treatment of PD within the desired time. Furthermore, the cerium content of the electrolyte membrane 80 is not limited to the above. The cerium content of the electrolyte membrane 80 can also be greater than 5 μg / cm³. 2 The amounts of metals such as cerium, platinum, and manganese contained in the electrolyte membrane 80 can be detected, for example, by ICP (Inductively Coupled Plasma) measurement.

[0066] According to the above embodiment, in at least one of the following scenarios—during startup or continuous operation of the water electrolysis system 1 where there is a concern about poisoning of the water electrolysis chamber 22—the control device 70 can restore the electrolysis performance of the water electrolysis chamber 22 by executing a potential change processing PF. Thus, in the water electrolysis system 1, the reduction in the amount of oxygen and hydrogen generated and the reduction in generation efficiency can be suppressed.

[0067] Furthermore, according to the above embodiment, the control device 70 can restore the electrolytic performance of the water electrolysis chamber 22 by performing a potential change process PF at least once and no more than 30 times. Moreover, the control device 70 can also restore the electrolytic performance of the water electrolysis chamber 22 by performing a potential change process PF at least once and no more than 18 times. Thus, the control device 70 can restore the electrolytic performance of the water electrolysis chamber 22 in a shorter time. Furthermore, the control device 70 can also restore the electrolytic performance of the water electrolysis chamber 22 by performing a potential change process PF at least once and no more than 6 times. Thus, the control device 70 can restore the electrolytic performance of the water electrolysis chamber 22 in a shorter time.

[0068] Furthermore, according to the above embodiment, the control device 70 can restore the electrolytic performance of the water electrolysis chamber 22 by performing the potential change processing PF in a manner that reduces the total time of the potential change processing PF to within 150 minutes. Moreover, the control device 70 can also restore the electrolytic performance of the water electrolysis chamber 22 by performing the potential change processing PF in a manner that reduces the total time of the potential change processing PF to within 90 minutes. Thus, the control device 70 can restore the electrolytic performance of the water electrolysis chamber 22 in a shorter time. Furthermore, the control device 70 can also restore the electrolytic performance of the water electrolysis chamber 22 by performing the potential change processing PF in a manner that reduces the total time of the potential change processing PF to within 30 minutes. Thus, the control device 70 can restore the electrolytic performance of the water electrolysis chamber 22 in a shorter time.

[0069] Furthermore, according to the above embodiment, after the control device 70 stops supplying power to the water electrolysis chamber 22, it causes the hydrogen generated at the cathode 82 to permeate through the electrolyte membrane 80 and move from the cathode 82 to the anode 81. This allows the control device 70 to perform the potential reduction process (PD). At this time, the thickness of the electrolyte membrane 80 constituting the water electrolysis chamber 22 can also be 25 μm or less. Thus, the control device 70 can restore the electrolysis performance of the water electrolysis chamber 22 in a shorter time.

[0070] Furthermore, according to the above embodiment, the control device 70 can perform potential change processing PF by controlling at least one of the current value and voltage value when power is supplied to the water electrolysis chamber 22.

[0071] B. Other implementation methods:

[0072] The potential change processing PF may also include a first holding process, in which, after the potential rise processing PU, the first holding process holds the potential of the anode 81 at the first potential P1 for a predetermined period. Alternatively, the potential change processing PF may also include a second holding process, in which, after the potential fall processing PD, the second holding process holds the potential of the anode 81 at the second potential P2 for a predetermined period.

[0073] This disclosure is not limited to the embodiments described above, and can be implemented in various structures without departing from its spirit. For example, in order to solve some or all of the above-described problems, or to achieve some or all of the above-described effects, the technical features of the embodiments corresponding to the technical features in the various methods described in the summary section of the invention can be appropriately replaced or combined. In addition, any technical feature not stated to be necessary in this specification can be appropriately deleted.

Claims

1. A water electrolysis system that generates hydrogen and oxygen through the electrolysis of water, wherein, The water electrolysis system comprises: A water electrolysis chamber comprising an anode, a cathode, and an electrolyte membrane sandwiched between the anode and the cathode; and The control device controls the power supplied to the water electrolysis chamber. The control device performs a potential variation process that causes a change in the potential of the anode during at least one of the start-up and continuous operation of the water electrolysis system. The potential variation process includes a potential reduction process that lowers the potential of the anode to a predetermined potential.

2. The water electrolysis system according to claim 1, wherein, The control device performs the potential change processing more than once and less than 30 times.

3. The water electrolysis system according to claim 1, wherein, After the control device stops supplying power to the water electrolysis chamber, it causes the hydrogen generated at the cathode to permeate through the electrolyte membrane and move from the cathode to the anode, thereby performing the potential reduction process.

4. The water electrolysis system according to claim 1, wherein, The control device performs the potential variation processing by controlling at least one of the current value and voltage value when power is supplied to the water electrolysis chamber.

5. The water electrolysis system according to claim 1, wherein, The thickness of the electrolyte membrane is less than 25 μm.

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