JP5421860B2 - Water electrolysis equipment shutdown method - Google Patents

Description

  In the present invention, a power feeding body is provided on both sides of the electrolyte membrane, and by applying an electrolysis voltage between the power feeding bodies, water is electrolyzed to generate oxygen in the anode side electrolysis chamber, and in the cathode side electrolysis chamber. The present invention relates to a method for stopping operation of a water electrolysis apparatus that generates hydrogen at a pressure higher than normal pressure.

  For example, in a polymer electrolyte fuel cell, a fuel gas (a gas containing mainly hydrogen, such as hydrogen gas) is supplied to the anode side electrode, while an oxidant gas (mainly containing oxygen) is supplied to the cathode side electrode. By supplying a gas (for example, air), direct current electric energy is obtained.

  In general, a water electrolysis apparatus is employed to produce hydrogen gas that is a fuel gas. This water electrolysis apparatus uses a solid polymer electrolyte membrane (ion exchange membrane) in order to decompose water and generate hydrogen (and oxygen). Electrode catalyst layers are provided on both sides of the solid polymer electrolyte membrane to form an electrolyte membrane / electrode structure, and a power feeder is provided on both sides of the electrolyte membrane / electrode structure. It is configured. That is, the unit is configured substantially in the same manner as the above fuel cell.

  Thus, in a state where a plurality of units are stacked, a voltage is applied to both ends in the stacking direction, and water is supplied to the anode side. For this reason, water is decomposed and hydrogen ions (protons) are generated on the anode side of the electrolyte membrane / electrode structure, and the hydrogen ions permeate the solid polymer electrolyte membrane and move to the cathode side to bond with electrons. Thus, hydrogen is produced. On the other hand, on the anode side, oxygen produced together with hydrogen ions is discharged from the unit with excess water.

  In this type of water electrolysis apparatus, since the pressure of hydrogen and oxygen generated is generally low, it is necessary to pressurize using a gas compressor, and there is a problem that the equipment becomes large and the cost increases. .

  Therefore, it is desired to obtain hydrogen and oxygen at a desired pressure without using a gas compressor. For this reason, for example, a hydrogen / oxygen gas generator disclosed in Patent Document 1 is known.

  This Patent Document 1 discloses a hydrogen for generating hydrogen gas and oxygen gas by directly electrolyzing pure water by a water electrolysis cell having an anode chamber and a cathode chamber separated by a diaphragm such as a solid polymer electrolyte. -It relates to an oxygen gas generator.

  The hydrogen / oxygen gas generator is provided with a communication port that communicates with the outside at the lower part of the anode chamber, and an oxygen outlet pipe that guides oxygen gas generated by electrolysis of pure water upward from the anode chamber side. An electrolysis cell and the water electrolysis cell are accommodated and supported in a state where the water electrolysis cell is immersed in pure water, and an oxygen gas separation chamber in which the upper opening end of the oxygen outlet pipe is opened is formed at the upper part. A pure water container, a gas-liquid separator connected to a hydrogen lead-out pipe for leading hydrogen gas generated by electrolysis of pure water from the upper part of the cathode chamber of the water electrolysis cell to the outside of the pure water container, and the oxygen gas separation First gas pressure detection means for detecting the pressure of oxygen gas accumulated in the upper part of the chamber, second gas pressure detection means for detecting the pressure of hydrogen gas accumulated in the upper part of the gas-liquid separator, oxygen Remove the oxygen gas that accumulates at the top of the gas separation chamber Detected by the first and second gas pressure detecting means, the second gas piping system for taking out the hydrogen gas accumulated in the upper portion of the gas-liquid separator, and the first and second gas pressure detecting means. Based on the detected pressure value, the first and second gas piping systems are controlled to control the pressure of the oxygen gas accumulated in the upper portion of the oxygen gas separation chamber and the pressure of the hydrogen gas accumulated in the upper portion of the gas-liquid separation device, respectively. Gas pressure control means, a DC power supply for supplying power to the water electrolysis cell, and the DC power supply is controlled so that the hydrogen gas pressure or the oxygen gas pressure is supplied to the water electrolysis cell so as to become a predetermined pressure. And a power control device for controlling power to be generated.

  In such a configuration, for example, the difference (differential pressure) between the oxygen gas pressure in the oxygen gas separation chamber and the hydrogen gas pressure in the gas-liquid separation chamber can be controlled to be within a predetermined small range, It is also possible to prevent the breakage of the diaphragm such as the solid polymer electrolyte membrane and the occurrence of gas leakage from the seal portion. Accordingly, the generated gas pressure can be set to a desired high pressure without causing the diaphragm to be broken due to the differential pressure or the gas leakage from the seal portion.

JP-A-8-193287

  By the way, in the above hydrogen / oxygen gas generator, when the operation is stopped (the supply of generated hydrogen is finished), the pressure difference between both sides of the solid polymer electrolyte membrane is released in order to protect the solid polymer electrolyte membrane and the seal member. There is a need to.

  However, if the operation is stopped while the hydrogen pressure is reduced to normal pressure, internal parts exposed to high-pressure hydrogen, for example, the solid polymer electrolyte membrane and the seal member will be damaged. There's a problem. That is, the larger the volume expansion rate of hydrogen due to reduced pressure, the higher the probability of damage to the solid polymer electrolyte membrane and the seal member due to the expansion of hydrogen present inside the solid polymer electrolyte membrane and the seal member. .

  The present invention solves this type of problem, and can reduce the expansion of hydrogen inside the electrolyte membrane and the seal member when the operation is stopped, thereby damaging the electrolyte membrane and the seal member as much as possible. It is an object of the present invention to provide a water electrolysis apparatus shutdown method that can be avoided.

  In the present invention, a power feeding body is provided on both sides of the electrolyte membrane, and by applying an electrolysis voltage between the power feeding bodies, water is electrolyzed to generate oxygen in the anode side electrolysis chamber, and in the cathode side electrolysis chamber. The present invention relates to a method for stopping the operation of a water electrolysis apparatus that generates hydrogen at a pressure higher than normal pressure.

In this operation stopping method, the application of the electrolysis voltage is stopped to stop the water electrolysis treatment by the water electrolysis apparatus, the step of reducing the pressure of the high-pressure hydrogen generated in the cathode-side electrolysis chamber, pressure, when it becomes less且single set pressure P _H at a pressure above atmospheric pressure, and a step of terminating said vacuum the set pressure P _H of the high-pressure hydrogen at stops, at stop Assuming that the pressure P _O of oxygen, the hydrogen concentration N% in oxygen in the equilibrium state, the cathode side volume V _H and the anode side volume V _O , P _H <P _O /(1-0.01×N)×{1+0 .01 × N (V _O / V _H )} .

  According to the present invention, the high-pressure hydrogen generated in the cathode-side electrolysis chamber is maintained at a pressure exceeding the atmospheric pressure in a state where the operation of the water electrolysis apparatus is stopped. For this reason, the expansion rate of hydrogen can be kept low, and the volume expansion of the hydrogen inside the electrolyte membrane and the seal member can be suppressed. Therefore, damage to the electrolyte membrane and the seal member can be avoided as much as possible.

Moreover, in a state in which the operation of the water electrolysis apparatus is stopped, the high pressure hydrogen generated on the cathode side electrolysis chamber is maintained below set pressure P _H. This allows hydrogen to leak through the electrolyte membrane from the cathode side to the anode side during the outage period, but the hydrogen concentration in oxygen on the anode side in the equilibrium state can be maintained below the desired concentration. become.

BRIEF DESCRIPTION OF THE DRAWINGS It is schematic structure explanatory drawing of the water electrolysis apparatus to which the operation stop method which concerns on the 1st Embodiment of this invention is applied. It is a disassembled perspective explanatory drawing of the unit cell which comprises the said water electrolysis apparatus. It is sectional explanatory drawing of the said unit cell. It is explanatory drawing of the said operation stop method. It is explanatory drawing of the pressure reduction process of high pressure hydrogen. It is schematic structure explanatory drawing of the water electrolysis apparatus to which the operation stop method of the water electrolysis apparatus which concerns on the 2nd Embodiment of this invention is applied.

  As shown in FIG. 1, the water electrolysis apparatus 10 to which the operation method according to the first embodiment of the present invention is applied is obtained by electrolyzing pure water to generate high-pressure hydrogen (higher than normal pressure, for example, 1 MPa or more). ) And pure water generated from city water is supplied via the pure water supply mechanism 14, and the pure water is supplied to the water electrolysis mechanism 12 and from the water electrolysis mechanism 12. A water circulation mechanism 16 that circulates and supplies excess water to the water electrolysis mechanism 12 and a controller (control unit) 18 are provided.

  The water electrolysis mechanism 12 constitutes a high-pressure hydrogen production apparatus (cathode side pressure> anode side pressure), and a plurality of unit cells 20 are stacked. At one end in the stacking direction of the unit cells 20, a terminal plate 22a, an insulating plate 24a, and an end plate 26a are sequentially arranged outward. Similarly, a terminal plate 22b, an insulating plate 24b, and an end plate 26b are sequentially arranged on the other end in the stacking direction of the unit cells 20 toward the outside. The end plates 26a and 26b are integrally clamped and held.

  Terminal portions 28a and 28b are provided on the side portions of the terminal plates 22a and 22b so as to protrude outward. The terminal portions 28a and 28b are electrically connected to an electrolysis power source (electrolysis power source) 30 via wirings 29a and 29b. The terminal part 28 a on the anode (anode) side is connected to the positive electrode of the electrolysis power supply 30, while the terminal part 28 b on the cathode (cathode) side is connected to the negative electrode of the electrolysis power supply 30.

  As shown in FIG. 2, the unit cell 20 includes a disc-shaped electrolyte membrane / electrode structure 32, and an anode separator 34 and a cathode separator 36 that sandwich the electrolyte membrane / electrode structure 32. The anode-side separator 34 and the cathode-side separator 36 have a disk shape, and are made of, for example, a carbon member or the like, or are used for corrosion protection on a steel plate, a stainless steel plate, a titanium plate, an aluminum plate, a plated steel plate, or a metal surface thereof. The metal plate that has been subjected to the above surface treatment is press-molded or cut and subjected to a corrosion-resistant surface treatment.

  The electrolyte membrane / electrode structure 32 includes, for example, a solid polymer electrolyte membrane 38 in which a perfluorosulfonic acid thin film is impregnated with water, an anode-side power feeder 40 and a cathode provided on both surfaces of the solid polymer electrolyte membrane 38. Side power supply body 42.

  An anode electrode catalyst layer 40a and a cathode electrode catalyst layer 42a are formed on both surfaces of the solid polymer electrolyte membrane 38. The anode electrode catalyst layer 40a uses, for example, a Ru (ruthenium) -based catalyst, while the cathode electrode catalyst layer 42a uses, for example, a platinum catalyst.

  The anode-side power supply body 40 and the cathode-side power supply body 42 are made of, for example, a sintered body (porous conductor) of spherical atomized titanium powder. The anode-side power supply body 40 and the cathode-side power supply body 42 are provided with a smooth surface portion that is etched after grinding, and the porosity is set within a range of 10% to 50%, more preferably 20% to 40%. Is done.

  The outer peripheral edge of the unit cell 20 communicates with each other in the direction of arrow A, which is the stacking direction, to supply water (pure water) 46, oxygen generated by the reaction, and used water A discharge communication hole 48 for discharging water and a hydrogen communication hole 50 for flowing hydrogen (high-pressure hydrogen) generated by the reaction are provided.

  As shown in FIGS. 2 and 3, a supply passage 52 a that communicates with the water supply communication hole 46 and a discharge passage 52 b that communicates with the discharge communication hole 48 are provided at the outer peripheral edge of the anode separator 34. A first flow path (anode-side electrolytic chamber) 54 communicating with the supply passage 52a and the discharge passage 52b is provided on the surface 34a of the anode-side separator 34 facing the electrolyte membrane / electrode structure 32. The first flow path 54 is provided in a range corresponding to the surface area of the anode-side power feeding body 40, and includes a plurality of flow path grooves, a plurality of embosses, and the like (see FIGS. 1 and 3).

  A discharge passage 56 communicating with the hydrogen communication hole 50 is provided at the outer peripheral edge of the cathode separator 36. A second flow path (cathode side electrolytic chamber) 58 communicating with the discharge passage 56 is formed on the surface 36 a of the cathode separator 36 facing the electrolyte membrane / electrode structure 32. The second flow path 58 is provided within a range corresponding to the surface area of the cathode power supply body 42 and is configured by a plurality of flow path grooves, a plurality of embosses, and the like (see FIGS. 1 and 3).

  The seal members 60a and 60b are integrated with each other around the outer peripheral ends of the anode side separator 34 and the cathode side separator 36. The seal members 60a and 60b include, for example, EPDM, NBR, fluorine rubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber, chloroprene, acrylic rubber, or other seal materials, cushion materials, or packing materials. Used.

  As shown in FIG. 3, on the surface 34a of the anode-side separator 34 facing the electrolyte membrane / electrode structure 32, the first seal member 62a is wound around the outside of the first flow path 54 and the anode-side power feeder 40. A first seal groove 64a for disposing is formed. In the surface 34a, first seal grooves 64b, 64c, and 64d for circulating the outer sides of the water supply communication hole 46, the discharge communication hole 48, and the hydrogen communication hole 50 to dispose the first seal members 62b, 62c, and 62d. Is formed. The first seal members 62a to 62d are, for example, O-rings.

  A second seal member 66a is disposed on the surface 36a of the cathode separator 36 facing the electrolyte membrane / electrode structure 32 around the outside of the second flow path 58 and the cathode power supply body 42. Two seal grooves 68a are formed.

  As shown in FIGS. 2 and 3, the second seal members 66b, 66c and 66d are arranged on the surface 36a around the outside of the water supply communication hole 46, the discharge communication hole 48 and the hydrogen communication hole 50. The second seal grooves 68b, 68c and 68d are formed. The second seal members 66a to 66d are, for example, O-rings.

  As shown in FIG. 1, the water circulation mechanism 16 includes a circulation pipe 72 that communicates with the water supply communication hole 46 of the water electrolysis mechanism 12, and the circulation pipe 72 includes a circulation pump 74, an ion exchanger 76, and an oxygen side gas. A liquid separator 78 is provided.

  One end of a return pipe 80 communicates with the upper part of the oxygen side gas-liquid separator 78, and the other end of the return pipe 80 communicates with the discharge communication hole 48 of the water electrolysis mechanism 12. The oxygen-side gas-liquid separator 78 includes a water level gauge 84 for detecting the water level stored in the chamber 78 a, a blower 86 for supplying air to the chamber 78 a, and a reverse disposed downstream of the blower 86. A stop valve 88 is provided.

  The oxygen side gas / liquid separator 78 includes a pure water supply pipe 90 connected to the pure water supply mechanism 14 and an oxygen exhaust pipe for discharging oxygen separated from the pure water by the oxygen side gas / liquid separator 78. 92 are connected. A check valve 94 and a solenoid valve 96 are disposed in the oxygen exhaust pipe 92.

  One end of a high-pressure hydrogen pipe 98 is connected to the hydrogen communication hole 50 of the water electrolysis mechanism 12, and the hydrogen-side gas-liquid separator 100 is connected to the high-pressure hydrogen pipe 98. A drain pipe 102 is connected to the lower end of the hydrogen-side gas-liquid separator 100, and a drain electromagnetic valve 104 is disposed in the drain pipe 102.

  The hydrogen side gas-liquid separator 100 is provided with a water level meter 106 that detects the water level of water stored in the chamber 100a. One end of a high-pressure hydrogen supply pipe 108 is connected to the upper part of the hydrogen-side gas-liquid separator 100, and a hydrogen dehumidifier 110 and a back pressure valve 112 are disposed in the high-pressure hydrogen supply pipe 108. Although not shown, the high-pressure hydrogen supply pipe 108 is connected to a high-pressure hydrogen supply unit, for example, a high-pressure tank or a fuel cell vehicle.

  A decompression pipe 98a branches from the high-pressure hydrogen pipe 98, and a back pressure valve 114 and an electromagnetic valve 116 are disposed in the decompression pipe 98a.

  The operation of the water electrolysis apparatus 10 configured as described above will be described below.

  First, when the water electrolysis apparatus 10 is started, pure water generated from city water is supplied to the oxygen-side gas-liquid separator 78 constituting the water circulation mechanism 16 through the pure water supply mechanism 14.

  In the water circulation mechanism 16, pure water is supplied to the water supply communication hole 46 of the water electrolysis mechanism 12 through the circulation pipe 72 under the action of the circulation pump 74. On the other hand, an electrolytic voltage is applied to the terminal portions 28a and 28b of the terminal plates 22a and 22b through an electrolysis power supply 30 that is electrically connected.

  Therefore, as shown in FIG. 2, in each unit cell 20, water is supplied from the water supply communication hole 46 to the first flow path 54 of the anode-side separator 34, and this water flows along the anode-side power feeder 40. Moving.

  Accordingly, water is decomposed by electricity in the anode electrode catalyst layer 40a, and hydrogen ions, electrons, and oxygen are generated. Hydrogen ions generated by this anodic reaction permeate the solid polymer electrolyte membrane 38 and move to the cathode electrode catalyst layer 42a side, and combine with electrons to obtain hydrogen.

  For this reason, hydrogen flows along the second flow path 58 formed between the cathode side separator 36 and the cathode side power supply body 42. This hydrogen flows through the hydrogen communication hole 50 and can be taken out of the water electrolysis apparatus 10, and is supplied with water by the set pressure (for example, 35 MPa) of the back pressure valve 112 disposed in the high-pressure hydrogen supply pipe 108. The pressure is maintained higher than that of the communication hole 46.

  On the other hand, oxygen generated by the reaction and used water flow in the first flow path 54, and these are discharged along the discharge communication hole 48 to the return pipe 80 of the water circulation mechanism 16 (FIG. 1). The used water and oxygen are introduced into the oxygen-side gas-liquid separator 78 and separated, and then the water is supplied from the circulation pipe 72 through the ion exchanger 76 via the circulation pump 74 to the water supply communication hole 46. To be introduced. Oxygen separated from the water is discharged to the outside from the oxygen exhaust pipe 92.

  Next, a method for stopping operation of the water electrolysis apparatus 10 according to the first embodiment of the present invention will be described below.

First, the set pressure P _H of the high pressure hydrogen serving as a reference for stopping the operation of the water electrolysis device 10 is set in advance. Here, the pressure P _O of oxygen at the time of stopping, the hydrogen concentration N% in oxygen in the equilibrium state, the cathode side volume V _H and the anode side volume V _O are set. Specifically, the hydrogen concentration N% is preferably 4%, for example.

As shown in FIG. 4, the cathode-side volume V _H includes a hydrogen channel system including the second channel 58 in the water electrolysis mechanism 12, a high-pressure hydrogen pipe 98, a chamber 100 a of the hydrogen-side gas-liquid separator 100, and hydrogen dehumidification. The total volume of the high-pressure hydrogen supply pipe 108 extending from the machine 110 to the back pressure valve 112. Anode volume V _O is the combined volume of the oxygen discharge pipe 92 leading to the solenoid valve 96 from the chamber 78a and the chamber 78a of the oxygen-side gas-liquid separator 78. The volume of the chamber 78a and the volume of the chamber 100a can be calculated from the detection results of the water level meters 84 and 106, for example.

Therefore, the pressure P _EQ on the cathode side (hydrogen generation side) and anode side (oxygen generation side) in an equilibrium state is calculated from P _EQ = (V _H × P _H + V _O × P _O ) / (V _H + V _O ). Is done. On the other hand, on the anode side, hydrogen volume / (hydrogen + oxygen) volume = (P _EQ -P _O ) / P _EQ <0.01 × N is obtained.

Furthermore, P _H <P _O /(1-0.01×N)×{1+0.01×N(V _O / V _H )} is obtained from the above two formulas.

When water electrolysis process by water electrolysis mechanism 12 is stopped, the pressure of the high pressure hydrogen is and reduced to below the set pressure P _H at a pressure above atmospheric pressure. Specifically, the pressure of the back pressure valve 114 is set to the set pressure P _H.

Next, as shown in FIG. 4, when the water electrolysis process is stopped by the water electrolysis apparatus 10, the voltage application from the electrolysis power supply 30 is stopped and the driving of the circulation pump 74 is stopped. Further, when the electromagnetic valve 116 disposed in the depressurization pipe 98a is opened, the decompression process is performed in the high-pressure hydrogen path including the second flow path 58 as shown in FIG. Then, the pressure of high-pressure hydrogen path, when it is reduced to a set pressure P _H, decompression processing is completed back pressure valve 114 is closed.

  In this case, in the first embodiment, high-pressure hydrogen generated in the second flow path (cathode side electrolysis chamber) 58 in a state where the operation of the water electrolysis mechanism 12 is stopped is maintained at a pressure exceeding the atmospheric pressure. Yes. For this reason, the expansion rate of hydrogen can be kept low, and the volume expansion of the hydrogen inside the solid polymer electrolyte membrane 38 and the first seal member 62d can be suppressed. Therefore, it is possible to avoid the damage of the solid polymer electrolyte membrane 38 and the first seal member 62d as much as possible.

Moreover, in a state in which the operation of the water electrolysis unit 12 is stopped, the high pressure hydrogen generated in the second flow path 58 is maintained at the set pressure P _H is set on the basis of the concentration of hydrogen to oxygen leaking to the anode side ing. Thereby, during the stop period, although hydrogen leaks through the solid polymer electrolyte membrane 38 from the cathode side to the anode side, the hydrogen concentration in oxygen on the anode side in the equilibrium state is less than a desired concentration N%. Can be maintained.

  FIG. 6 is a schematic configuration explanatory diagram of a water electrolysis apparatus 120 to which the operation method according to the second embodiment of the present invention is applied.

  In addition, the same referential mark is attached | subjected to the component same as the water electrolysis apparatus 10 which concerns on 1st Embodiment, and the detailed description is abbreviate | omitted.

In the water electrolysis apparatus 120, a pressure detection sensor 122 is provided in place of the back pressure valve 114 in the middle of the decompression pipe 98a. The pressure detection sensor 122 detects that the hydrogen pressure in the de-pressure pipe 98a is equal to or less than the set pressure P _H, and sends a detection signal to the controller 18.

Therefore, controller 18, by closing the solenoid valve 116, a high-pressure hydrogen generated in the second flow path 58 is maintained and below the set pressure P _H at a pressure above atmospheric pressure.

  Thus, in the second embodiment, damage to the solid polymer electrolyte membrane 38 and the first seal member 62d is avoided as much as possible, and the hydrogen concentration in oxygen on the anode side in the equilibrium state is set to a desired concentration. An effect similar to that of the first embodiment described above can be obtained, such as being able to maintain below N%.

  Instead of the back pressure valve 114, a flow rate adjustment valve, an MFC (mass flow controller), or the like may be employed.

DESCRIPTION OF SYMBOLS 10, 120 ... Water electrolysis apparatus 12 ... Water electrolysis mechanism 14 ... Pure water supply mechanism 16 ... Water circulation mechanism 18 ... Controller 20 ... Unit cell 30 ... Power source for electrolysis 32 ... Electrolyte membrane and electrode structure 34 ... Anode side separator 36 ... Cathode Side separator 38 ... solid polymer electrolyte membrane 40 ... anode side power supply body 42 ... cathode side power supply body 46 ... water supply communication hole 48 ... discharge communication hole 50 ... hydrogen communication hole 54, 58 ... flow path 56 ... discharge passages 62a to 62d , 66a to 66d ... sealing member 72 ... circulation pipe 74 ... circulation pump 78 ... oxygen side gas-liquid separator 78a, 100a ... chamber 80 ... return pipe 84, 106 ... water level gauge 90 ... pure water supply pipe 92 ... oxygen exhaust pipe 94 ... Check valve 96, 116 ... Solenoid valve 98 ... High-pressure hydrogen pipe 98a ... Depressurization pipe 100 ... Hydrogen-side gas-liquid separator 102 ... Drain pipe 108 ... High-pressure water Element supply piping 112, 114 ... back pressure valve 122 ... pressure detection sensor

Claims (1)

A power feeding body is provided on both sides of the electrolyte membrane, and by applying an electrolysis voltage between the power feeding bodies, water is electrolyzed to generate oxygen in the anode-side electrolysis chamber, and in the cathode-side electrolysis chamber than normal pressure. A method for shutting down a water electrolyzer that generates high-pressure hydrogen,
Stopping water electrolysis treatment by the water electrolysis device by stopping application of the electrolysis voltage ;
Reducing the pressure of the high-pressure hydrogen generated in the cathode-side electrolysis chamber;
When the pressure of the high pressure hydrogen, became less且single set pressure P _H at a pressure above atmospheric pressure, a step of terminating said vacuum
I have a,
The set pressure P _H of the high-pressure hydrogen at stop, the pressure P _O of the oxygen at the time of stopping, the hydrogen concentration N% of oxygen at equilibrium, when the cathode-side volume V _H and anode volume V _{O, P H <P O /(1-0.01×N)×{1+0.01×N(V O /} V H) shutdown method of a water electrolysis apparatus characterized by have a relationship}.

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