CN116555791A - Electrochemical reaction device and electrochemical reaction method - Google Patents

Abstract

The invention provides an electrochemical reaction device and an electrochemical reaction method. An electrochemical reaction device according to an embodiment includes: an electrochemical reaction cell including a 1 st electrode having a 1 st flow path, a 2 nd electrode having a 2 nd flow path, and a separator sandwiched between the 1 st electrode and the 2 nd electrode; a liquid tank for storing the liquid to be treated in the 2 nd flow path supplied to the 2 nd electrode; a 1 st piping connecting the inlet of the 2 nd flow path and the liquid tank; a 2 nd piping connecting the outlet of the 2 nd flow path and the liquid tank; and a reverse flow suppressing means provided in the 2 nd pipe for preventing reverse flow of the liquid to be treated flowing in the 2 nd pipe or reducing the reverse flow rate.

Description

Electrochemical reaction device and electrochemical reaction method

This application is based on Japanese Patent Application No. 2022-011964 (filing date: 01/28/2022) and Japanese Patent Application No. 2022-118767 (filing date: 07/26/2022), and enjoys priority from the above applications. This application incorporates the entire content of this application by referring to the above application.

technical field

Embodiments of the present invention relate to an electrochemical reaction device and an electrochemical reaction method.

Background technique

A water electrolysis device that generates hydrogen (H ₂ ) and oxygen (O ₂ ) by electrolyzing water (H ₂ O) is known as a representative example of an electrochemical reaction device such as an electrolysis device. The water electrolysis device includes, for example, an electrolytic cell including an anode, a cathode, and a separator such as a solid polymer electrolyte membrane (Polymer Electrolyte Membrane: PEM) sandwiched between the anode and the cathode. In the water electrolysis device, hydrogen (H ₂ ) is generated at the cathode and oxygen (O ₂ ) is generated at the anode by electrolyzing water (H ₂ O). A water electrolyzer (PEM type water electrolyzer) using such a solid polymer electrolyte membrane (PEM) as a diaphragm has the characteristics of low operating temperature and high hydrogen purity. However, a water electrolyzer including a diaphragm such as a PEM type water electrolyzer has a problem that its performance tends to deteriorate when it is started and stopped. Such a problem is not limited to a water electrolytic cell, but also becomes a problem in an electrolytic cell and an electrolysis device (electrochemical reaction device) having a diaphragm.

Contents of the invention

The problem to be solved by the present invention is to provide an electrochemical reaction device and an electrochemical reaction method capable of suppressing performance degradation during start-stop operations.

An electrochemical reaction device according to an embodiment includes: an electrochemical reaction tank including a first electrode having a first flow path, a second electrode having a second flow path, and an electrode sandwiched between the first electrode and the second electrode. a holding diaphragm; a liquid tank for storing the liquid to be treated in the second flow path supplied to the second electrode; a first pipe connecting the inlet of the second flow path and the liquid tank , and the liquid to be treated is supplied to the second flow path; the second pipe is connected to the outlet of the second flow path and the liquid tank, and the liquid to be treated is returned to the liquid tank a tank; and a backflow suppression mechanism provided on the second pipe for preventing backflow or reducing a backflow velocity of the liquid to be treated flowing in the second pipe.

Description of drawings

FIG. 1 is a diagram showing the configuration of an electrochemical reaction cell and the connection structure between the electrochemical reaction cell and a power source in the electrochemical reaction device according to the embodiment.

FIG. 2 is a diagram showing an electrochemical reaction device according to the first embodiment.

FIG. 3 is an enlarged view showing a part of the electrochemical reaction device according to the first embodiment.

4 is a graph showing a comparison between the specific resistance of water when the electrochemical reaction device according to the first embodiment is stopped and the specific resistance of water when the electrochemical reaction device without a check valve is stopped.

FIG. 5 is a graph showing a comparison of the voltage change over time of the electrochemical reaction device according to the first embodiment and the voltage change over time of the electrochemical reaction device having no check valve.

Fig. 6 is a diagram showing an electrochemical reaction device according to a second embodiment.

Fig. 7 is a diagram showing part of a first example of an electrochemical reaction device according to a second embodiment.

Fig. 8 is a diagram showing part of a second example of the electrochemical reaction device according to the second embodiment.

Fig. 9 is a diagram showing an electrochemical reaction device according to a third embodiment.

FIG. 10 is a diagram showing an electrochemical reaction device according to a fourth embodiment.

Fig. 11 is a diagram showing an electrochemical reaction device according to a fifth embodiment.

Fig. 12 is a diagram showing an electrochemical reaction device according to a sixth embodiment.

Fig. 13 is a diagram showing a modified example of the electrochemical reaction device shown in Fig. 12 .

FIG. 14 is a diagram showing an example of an electrochemical reaction device according to a seventh embodiment.

Fig. 15 is a diagram showing another example of the electrochemical reaction device according to the seventh embodiment.

(Symbol Description)

1: Electrochemical reaction cell (electrolyzer), 2: 1st electrode, 3: 2nd electrode, 4: Diaphragm, 12: 1st flow path, 13: 2nd flow path, 20: Electrochemical reaction device (electrolysis device ), 22: water tank, 23: pure water manufacturing device, 24: first piping, 25: second piping, 26: pump, 27: ultrapure water manufacturing device, 28: check valve, 29: liquid level sensor, 31: U-shaped piping, 32: gas supply part, 33: long piping, 41: electrochemical reaction cell stack, 46: overflow wall, 47: water tank with overflow structure, 51: gas-liquid Separation tank (second water tank), 53: valve.

Detailed ways

Hereinafter, an electrochemical reaction device according to an embodiment will be described with reference to the drawings. In each of the embodiments described below, substantially the same components are denoted by the same symbols, and descriptions thereof may be partially omitted. The drawings are schematic diagrams, and the relationship between the thickness and planar dimensions, the ratio of the thickness of each part, and the like may differ from the actual ones. The symbols of "-" in the following description represent the range between an upper limit and a lower limit, respectively. In this case, each range includes an upper limit and a lower limit.

The configuration of the electrochemical reaction tank of the electrochemical reaction device according to the embodiment and the connection structure between the electrochemical reaction tank and the power supply will be described with reference to FIG. 1 . The electrochemical reaction cell 1 shown in FIG. 1 includes a first electrode 2 , a second electrode 3 , and a separator 4 sandwiched between the first electrode 2 and the second electrode 3 . The separator 4 has, for example, a solid polymer electrolyte membrane (PEM). When using the electrochemical reaction cell 1 as a water electrolyzer, the first electrode 2 is a cathode (reduction electrode/hydrogen electrode), and the second electrode 3 is an anode (oxidation electrode/oxygen electrode). Hereinafter, the case of using the electrochemical reaction cell 1 as the water electrolysis cell will be mainly described, but it is not limited thereto. As the solid polymer electrolyte membrane of the separator 4, a proton-conducting membrane can be used.

As a constituent material of the proton conductive PEM, for example, a fluororesin having a sulfonic acid group can be used. Specific examples of such materials include Nafion (registered trademark), which is a fluororesin produced by sulfonation of tetrafluoroethylene from DuPont, Aciplex (registered trademark) manufactured by Asahi Kasei, and Flemion (registered trademark) manufactured by AGC Corporation. )wait. The separator 4 is not limited to a solid polymer electrolyte membrane, and may be an electrolyte membrane such as a hydrocarbon membrane containing an electrolyte component, or a membrane containing inorganic substances such as tungstic acid and phosphotungstic acid.

The anode, that is, the second electrode 3 , electrolyzes water (H ₂ O) through an oxidation reaction to generate hydrogen ions (H ⁺ ) and oxygen (O ₂ ). The cathode, that is, the first electrode 2 generates hydrogen (H ₂ ) by reducing hydrogen ions (H ⁺ ) generated at the anode. The cathode, that is, the first electrode 2 has a first catalyst layer 5 and a first power feeding layer 6 . The first catalyst layer 5 is arranged in contact with the separator 4 . The anode, that is, the second electrode 3 has a second catalyst layer 7 and a second power feeding layer 8 . The second catalyst layer 7 is arranged in contact with the separator 4 . A membrane electrode assembly (Membrane Electrode Assembly: MEA) 9 is formed by sandwiching a separator 4 such as a PEM between the first electrode 2 and the second electrode 3 .

As the cathode, that is, the first catalyst layer 5 of the first electrode 2, for example, metals such as platinum (Pt), silver (Ag), palladium (Pd) and an alloy containing at least one of Pt, Ag, and Pd (Pt alloy , Ag alloy, Pd alloy), etc. It is more preferable to use Pt and Pt alloys such as PtCo, PtFe, PtNi, PtPd, PtIr, PtRu, and PtSn for the first catalyst layer 5 . As the anode, that is, the second catalyst layer 7 of the second electrode 3, for example, iridium (Ir) oxide, ruthenium (Ru) oxide, palladium (Pd) oxide, Ir composite oxide, Ru composite oxide, Pd composite oxide, etc. can be used. oxides, etc. Examples of composite metals constituting Ir composite oxides and Ru composite oxides include titanium (Ti), niobium (Nb), vanadium (V), chromium (Cr), manganese (Mn), cobalt (Co), zinc (Zn ), zirconium (Zr), molybdenum (Mo), tantalum (Ta), Ru, Ir, Pd, etc. As the second catalyst layer 7, it is more preferable to use Ir oxide, Ir composite oxide, or the like.

As the first power feeding layer 6 of the first electrode 2 and the second power feeding layer 8 of the second electrode 3, a material having gas diffusivity and conductivity can be used. Specifically, a porous conductive member or the like is suitably used for the first power feeding layer 6 and the second power feeding layer 8 . As the first power feeding layer 6 and the second power feeding layer 8, porous metal members such as Ti, Ta, SUS, Ni, Pt, etc., metal felt, metal nonwoven fabric wrapped with metal fibers, carbon paper, carbon paper, etc. can be used. cloth etc. As the first power feeding layer 6 and the second power feeding layer 8 , it is preferable to use Ti, which is excellent in corrosion resistance, so that durability can be improved. In addition, durability can be further improved by plating these materials with gold or platinum.

The MEA 9 is sandwiched between the cathode separator 10 and the anode separator 11 , thereby constituting the electrochemical reaction cell 1 . The cathode separator 10 is provided with a first flow path 12 through which the reaction substance and the product substance flow. The anode separator 11 is provided with a second flow path 13 through which the reaction substance and the product substance flow. On the side surfaces of the first catalyst layer 5 and the first power supply layer 6 and the side surfaces of the second catalyst layer 7 and the second power supply layer 8, a sealing member 14 is arranged to prevent gas from the MEA 9 and the electrochemical reaction cell 1 or liquid leaks.

The electrochemical reaction cell 1 is not limited to a single cell structure, and may also have a stacked cell structure formed by stacking a plurality of electrochemical reaction cells 1 . The structure of the stacked tanks is not particularly limited, and can be appropriately selected according to desired voltage and reaction volume. When a plurality of electrochemical reaction cells 1 are used, it is not limited to a stacked cell structure, and a structure in which a plurality of electrochemical reaction cells 1 are planarly arranged may be used. In addition, grooves arranged in a plane may be further laminated. The number of single cells included in the electrochemical reaction cell 1 is not particularly limited, and can be selected appropriately.

As the reaction substance supplied to the electrochemical reaction cell 1 , for example, an aqueous solution containing at least one of water, hydrogen, modified gas, methanol, ethanol, formic acid, and the like can be used. When the electrochemical reaction cell 1 of the embodiment is a water electrolyzer, it is preferably pure water (such as pure water with a specific resistance of more than 0.01MΩ·cm and less than 5MΩ·cm) in the water electrolyzer, and more preferably ultrapure water ( For example, ultrapure water with a specific resistance of 17 MΩ·cm or more). The electrochemical reaction cell 1 in the embodiment is not limited to an electrolytic cell for electrolysis of water, and can be applied to various electrolytic cells as long as it is an electrochemical reaction cell that also uses an oxide as a catalyst, such as an electrolytic cell for carbon dioxide. In addition, the electrochemical reaction tank 1 is not limited to an electrolytic tank, and may be a fuel cell tank or the like.

The first electrode 2 and the second electrode 3 of the electrochemical reaction cell 1 are electrically connected to a voltage application mechanism (power supply) 15 . A voltage measurement unit 16 and a current measurement unit 17 are provided on a circuit electrically connecting the power supply 15 and the first electrode 2 and the second electrode 3 . The operation of the power supply 15 is controlled by the control unit 18 . The control unit 18 controls the power supply 15 to apply a voltage to the electrochemical reaction cell 1 . The voltage measuring unit 16 is electrically connected to the first electrode 2 and the second electrode 3 , and measures the voltage applied to the electrochemical reaction cell 1 . The measurement information is sent to the control unit 18 . The current measuring unit 17 is inserted into a voltage application circuit for the electrochemical reaction cell 1 , and measures the current flowing in the electrochemical reaction cell 1 . The measurement information is sent to the control unit 18 .

The control part 18 is comprised by computers, such as a PC and a microcomputer, for example, performs arithmetic processing on the data signal output from each part, and outputs necessary control signal to each constituent part. The control unit 18 also has a memory, and controls the output of the power supply 15 based on each piece of measurement information according to the program stored in the memory, and performs control such as applying voltage to the electrochemical reaction cell 1 or changing a load. When the electrochemical reaction cell 1 is used for a battery reaction, a voltage is applied to the electrochemical reaction cell 1 . When the electrochemical reaction cell 1 is used for a reaction other than a battery reaction, for example, a hydrogen generation reaction by electrolysis of water, an electrolysis reaction of carbon dioxide, etc., a voltage is applied to the electrochemical reaction cell 1 . The electrochemical reaction device of the embodiment is configured, for example, to apply a voltage between the first electrode 2 and the second electrode 3 to cause an electrochemical reaction.

(first embodiment)

Next, an electrochemical reaction device 20 according to a first embodiment including the electrochemical reaction tank 1 shown in FIG. 1 will be described with reference to FIG. 2 . Here, the configuration when the electrochemical reaction device 20 is applied to a water electrolysis device for electrolyzing water will be mainly described, but the electrochemical reaction device of the embodiment is not limited thereto, and may be a carbon dioxide electrolysis device or the like. The electrochemical reaction device (electrolysis device) 20 shown in FIG. water.

The water supply system 21 has a water tank 22 as a liquid tank for storing the liquid to be treated and supplied to the second flow path 13 of the second electrode 3 . A pure water manufacturing device 23 is connected to the water tank 22 , and pure water as a treatment stock solution can be supplied from the pure water manufacturing device 23 to the water tank 22 . As the pure water production device 23, for example, a reverse osmosis membrane (RO membrane) device can be used. Tap water W etc. can be supplied to the pure water manufacturing apparatus 23 as raw material water. The specific resistance of tap water W is about 0.01MΩ·cm@25°C or lower. If such water W is treated with a pure water manufacturing device 23 such as an RO membrane device, it is possible to manufacture a Pure water (treatment stock solution) with specific resistance. Such pure water can be supplied to the water tank 22 .

A first pipe 24 and a second pipe 25 are connected to the water tank 22 . The first pipe 24 is a supply pipe for supplying water to the second electrode 3 of the electrochemical reaction cell 1 , and is connected to the water tank 22 and the inlet IN of the second flow path 13 . A pump 26 and an ultrapure water manufacturing device 27 are provided in the first piping 24 which is the supply piping. As the ultrapure water production apparatus 27, for example, an ultrapure water apparatus using an ion exchange resin can be used. The pure water stored in the water tank 22 is sent to an ultrapure water production device 27 via a pump 26 . If pure water with a specific resistance in the range of 0.01 to 5MΩ·cm@25°C is treated with an ultrapure water manufacturing device 27 such as an ion exchange resin device, for example, a pure water with a specific resistance of 18.24MΩ·cm@25°C can be produced. The ultrapure water with a specific resistance above cm@25°C is used as the liquid to be treated. Such ultrapure water is fed into the inlet IN of the second flow path 13 of the second electrode 3 as the liquid to be treated, and while it flows through the second flow path 13, water is electrolyzed by the second electrode 3 as the anode. .

The outlet OUT of the second flow path 13 of the second electrode 3 is connected to a second pipe 25 for returning oxygen (O ₂ ) generated by water decomposition and excess water to the water tank 22 . The second pipe 25 is a return pipe (also referred to as an oxygen pipe) that returns oxygen (O ₂ ) generated by water decomposition and the remaining water to the water tank 22, and is connected to the outlet OUT of the second flow path 13 and the water Tank 22 on. The water tank 22 has a gas-liquid separation function, and oxygen (O ₂ ) separated in the water tank 22 can be recovered as needed. The water contained in the water tank 22 circulates through the first pipe 24 , the pump 26 , the ultrapure water production device 27 , the second flow path 13 , and the second pipe 25 . The second pipe 25 is provided with a check valve 28 as a backflow suppressing mechanism as will be described in detail later.

In the water electrolysis by the second electrode 3, oxygen (O ₂ ) and hydrogen ions (protons/H ⁺ ) are produced. Protons (H ⁺ ) are transported from the second electrode 3 to the first electrode 2 of the electrochemical reaction cell 1 through the separator 4 . Since water is also sent from the second electrode 3 to the first electrode 2 through the diaphragm 4, a water tank with a gas-liquid separation function can be connected to the outlet of the first flow path 12 of the first electrode 2 as required. The protons (H ⁺ ) transported to the first electrode 2 react with the electrons (e ⁻ ) reaching the first electrode 2 through the external circuit to generate hydrogen (H ₂ ). Hydrogen (H ₂ ) generated in the first electrode 2 is discharged to the outside from the first electrode 2 directly or through a water tank, and recovered.

Next, the operation of the electrochemical reaction device 20 shown in FIG. 2 will be described. When electrolyzing water, when a voltage is applied from an external power source to the second electrode 3 serving as an anode, water (H ₂ O) is electrolyzed, and a reaction of the following formula (1) occurs.

2H ₂ O→O ₂ +4H ⁺ +4e ^- (1)

Protons (H ⁺ ) generated at this time pass through the separator 4 and are transported to the first electrode 2 which is a cathode. In addition, electrons (e ⁻ ) reach the first electrode 2 through an external circuit. Hydrogen is generated in the first electrode 2 serving as a cathode by a reaction of the following formula (2).

4H ⁺ +4e ^- → 2H ₂ (2)

Hydrogen and oxygen can be produced by the reactions of the above formula (1) and formula (2).

As described above, the outlet OUT of the second flow path 13 of the second electrode 3 and the water tank 22 are connected via the second pipe 25 . In such a configuration, if no backflow suppression mechanism such as the check valve 28 is provided in the second piping 25, the pure water in the water tank 22 supplied from the pure water manufacturing device 23 may be present when the operation of the electrolysis device 20 is stopped. There is a possibility of backflow into the second electrode 3 through the second piping 25 and the second channel 13 or diffusion of impurities in a concentration gradient. If pure water flows into the second electrode 3, the pure water contained in the water tank 22 with a specific resistance in the range of 0.1 to 5 MΩ·cm also reaches the diaphragm 4 and the first electrode because the second electrode 3 is porous. Electrode 2. Small anion components, cation components, SiO ₂ and other fine particles contained in such pure water enter the inside of the separator 4, resulting in a decrease in ion conductivity, or by adsorption on the first electrode 2 and the second electrode 3. On the catalyst on the surface, the reaction area of the electrochemical reaction such as electrolysis is extremely reduced and other adverse effects. Such backflow of the pure water in the water tank 22 to the electrochemical reaction cell 1 is a factor that reduces the performance of the electrochemical reaction cell 1 .

Therefore, in the electrochemical reaction device (electrolysis device) 20 of the first embodiment, in the second piping 25 connecting the water tank 22 and the outlet OUT of the second flow path 13 of the second electrode 3, a backflow suppression mechanism is provided. There is a check valve 28 . When the operation of the electrolysis device 20 is stopped, the pure water in the water tank 22 can be prevented from flowing back to the second electrode 3 via the second pipe 25 and the second flow path 13 by the check valve 28 . By suppressing the reverse flow of the pure water in the water tank 22 to the second electrode 3, the electrochemical reaction device (electrolysis device) 20 can be stopped in a state where the second flow path 13 and the second electrode 3 are filled with ultrapure water. Therefore, the performance of the electrochemical reaction cell 1 when the electrochemical reaction device (electrolysis device) 20 is stopped can be maintained.

As the check valve 28 for suppressing the reverse flow of pure water in the water tank 22 to the second electrode 3, the lowest check differential pressure P (kPa) is preferably equal to or greater than the value represented by the following formula (3).

Δh×ρ×g(3)

Δh is "the height of the liquid surface in the water tank 22 - the height of the check valve 28", ρ is the density of the liquid, and g is the acceleration of gravity. By adopting the check valve 28 in which the lowest check differential pressure P is equal to or greater than the value represented by the formula (3), it is possible to effectively prevent the pure water in the water tank 22 from flowing back into the second electrode 3 when the operation of the electrolysis device 20 is stopped. . Examples of the check valve 28 having such a configuration include swing check valves, lift check valves such as smolensky check valves (also referred to as slow-closing check valves), wafer check valves, and ball check valves. return valve etc. On the other hand, a valve including a plurality of teardrop-shaped rings (so-called Tesla valves) in which the liquid flowing in the tube detours is not suitable.

In the electrochemical reaction device (electrolyzer) 20 of the first embodiment, the second pipe 25 provided with the check valve 28 is preferably connected to the water below the liquid surface of the water tank 22 , that is, under the water. The pure water manufacturing device 23 is based on, for example, the configuration shown in FIG. 3 , and supplies water W to the water tank 22 as raw water of water to be treated (water to be electrolyzed). The water tank 22 has a liquid level sensor 29 provided therein. The liquid level sensor may be a laser type liquid level gauge or the like provided outside the water tank 22 . When the liquid level in the water tank 22 falls below the lower limit value of the liquid level sensor 29 , the feed water pump 30 that supplies water W to the water tank 22 from the pure water manufacturing device 23 is activated to supply water into the water tank 22 . Therefore, it is preferable to connect the second pipe 25 to a position lower than the liquid level in the water tank 22 set by the liquid level sensor 29 .

By connecting the second pipe 25 to a position lower than the liquid level set by the liquid level sensor 29, the pure water in the water tank 22 can be suppressed by the check valve 28 while maintaining the liquid-tight state through the second pipe 25. countercurrent. Even when the second pipe 25 is connected at a position higher than the liquid surface, the backflow of water in the second pipe 25 can be suppressed. However, if the stop time becomes longer, the water remaining in the second piping 25 evaporates and the MEA 9 dries up. If it dries, the diaphragm 4 shrinks and becomes swollen when water is supplied again, and mechanical load is applied to the diaphragm 4 by repeating the dry-wet cycle, so the flow path blockage caused by the rupture or deformation of the diaphragm 4 occurs, and from the electrolytic cell 1 is also not preferable from the viewpoint of durability.

4 compares the specific resistance of water when the electrochemical reaction device (electrolysis device) 20 is stopped (when the current stops), and the specific resistance of water when the electrolysis device without a check valve is stopped. FIG. 5 shows the voltage change over time of the electrochemical reaction device (electrolysis device) 20 compared with the voltage change over time of the electrolysis device without a check valve. As shown in FIG. 4 , by providing the check valve 28 in the second piping 25 , it is possible to suppress a decrease in specific resistance due to the backflow of water in the water tank 22 to the second electrode 3 . Also, as shown in FIG. 5 , by providing the check valve 28 in the second piping 25 , it is possible to suppress performance degradation of the electrolytic cell 1 due to backflow of water in the water tank 22 .

(second embodiment)

An electrochemical reaction device 20 according to a second embodiment will be described with reference to FIGS. 6 to 8 . In the electrochemical reaction device 20 shown in FIG. 6, in the second pipe 25 connecting the water tank 22 and the outlet OUT of the second flow path 13 of the second electrode 3, there is a reverse U-shaped arrangement as a backflow suppression mechanism. U-shaped piping 31 (arranging upward in a convex shape). Other configurations are the same as those of the electrochemical reaction device 20 of the first embodiment shown in FIG. 2 . According to the U-shaped pipe 31 arranged in a reverse U-shape, when the water flowing in the second pipe 25 is stopped, as shown in _FIG . The gas and liquid are separated in the gas and stored in the upper part of the U-shaped pipe 31 to form the gas storage part G. By forming such a gas storage portion G in the U-shaped pipe 31 , the ultrapure water UW on the second electrode 3 side and the pure water PW on the water tank 22 side are separated. Therefore, the liquids in the water tank 22 and the second electrode 3 do not merge, and the pure water PW in the water tank 22 can be prevented from flowing back into the second electrode 3 .

The U-shaped piping 31 as the backflow suppression mechanism is an example of the backflow suppression piping, and the backflow suppression piping is not limited to U-shaped piping as long as it has a shape in which the gas storage part G can be formed by gas-liquid separation. . The backflow suppressing piping preferably has a shape that facilitates forming the gas storage portion G inside the piping and prevents natural leakage of gas in the gas storage portion G. Examples thereof include U-shaped piping 31 and V-shaped piping. When the gas in the gas-liquid mixed flow discharged from the second electrode 3 remains in the U-shaped pipe 31, all the gas leaks out from the second pipe 25 if the pump 26 is operated shortly after the electrolysis stops. In order to store the generated gas during electrolysis in the U-shaped pipe 31 as the gas storage part G, it is preferable to stop the pump 26 immediately after the gas generation by electrolysis stops.

Instead of forming the gas storage portion G by gas-liquid separation of the gas (such as O ₂ ) in the gas-liquid mixed flow discharged from the second electrode 3, for example, as shown in FIG. The gas supply unit 32 supplies gas to a portion forming the gas storage portion G of the U-shaped pipe 31 . The gas supplied from the gas supply unit 32 is not particularly limited, and may be oxygen (O ₂ ), which is a gas produced in electrolysis, or nitrogen (N ₂ ), argon (Ar), air, or the like. When gas is supplied from the external gas supply unit 32 , the pump 26 may be stopped within a range in which the liquid level of the gas-liquid mixed flow in the U-shaped pipe 31 does not drop.

In the case of using backflow suppression piping such as the U-shaped piping 31 , it is preferable to connect the second piping 25 to a position lower than the liquid level of the water tank 22 . The liquid level of the water tank 22 is set by the liquid level sensor similarly to the first embodiment. Thereby, the backflow of the pure water in the water tank 22 can be suppressed by the gas storage part G formed in the backflow suppressing pipe like the U-shaped pipe 31 while maintaining the liquid-tight state by the second pipe 25 . Thereby, the reduction of the characteristic, durability, etc. of the electrolytic cell 1 can be suppressed.

(third embodiment)

An electrochemical reaction device 20 according to a third embodiment will be described with reference to FIG. 9 . In the electrochemical reaction device 20 shown in FIG. 9 , a long pipe 33 is provided as a backflow suppressing pipe in the second pipe 25 connecting the water tank 22 and the outlet OUT of the second flow path 13 of the second electrode 3 . During operation of the device, generated oxygen and ultrapure water move to the water tank 22 through the second pipe 25 including the long pipe 33 . When the operation of the electrochemical reaction device 20 is stopped, pure water flows back from the water tank 22 into the second electrode 3 . Correspondingly, by sufficiently extending the length of the second piping 25 including the long piping 33 (for example, the shortest distance with respect to the second piping 25 is about several tens of times), the pure water can be extended from the water tank 22 to the second piping. Electrode 3 time.

An appropriate length of the second pipe 25 can be calculated using Fick's law from the impurity concentration of the water contained in the water tank 22 and the pipe diameter. That is to say, the impurity in the water can be calculated by using Fick's law to diffuse in the second pipe 25 and reach the length of the second electrode 3, so for example, by considering the time for stopping the electrochemical reaction device 20, the water reaching the second electrode 3 can be calculated by Fick's law. The length of the second pipe 25 including the long pipe 33 is set so that the specific resistance of the pipe is not lower than 5 MΩ·cm. When the stop period of operation is long, it is preferable to further extend the piping length. In this way, by extending the length of the second pipe 25 sufficiently by using the long pipe 33, the time for the pure water to reach the second electrode 3 from the water tank 22 is extended, thereby being able to keep the second flow path 13 and the second electrode 3 full for a long time. state of ultrapure water. Therefore, deterioration of the electrolytic cell 1 and the electrolytic device 20 can be suppressed.

(fourth embodiment)

An electrochemical reaction device 20 according to a fourth embodiment will be described with reference to FIG. 10 . FIG. 10 shows an electrochemical reactor stack 41 in which a plurality of electrochemical reactors shown in FIG. 1 are stacked. The other basic configurations are substantially the same as those of the electrochemical reaction device 20 shown in FIG. 2 . The difference between the electrochemical reaction device 20 shown in FIG. 2 and the electrochemical reaction device 20 shown in FIG. 10 will be mainly described below. Like the electrochemical reaction device 20 shown in FIG. 2 , the electrochemical reaction device 20 shown in FIG. 10 includes a water tank 22 as a liquid tank for storing the liquid to be treated to be supplied to the second flow path of the second electrode. A reverse osmosis membrane (RO membrane) device 42 and a carbon filter device 43 are connected to the water tank 22 as a pure water production device. On the upstream side of the carbon filter device 43, a solenoid valve 44 electrically connected to the liquid level sensor 29 provided in the water tank 22 is provided. When the liquid level in the water tank 22 measured by the liquid level sensor 29 is lower than the lower limit, the solenoid valve 44 is opened to supply pure water to the water tank 22 through the carbon filter device 43 and the RO membrane device 42 .

A pump 26 and an ion exchange resin device 45 as an ultrapure water production device are provided in the first pipe 24 which is a water supply pipe to the tank stack 41 . Ultrapure water having a specific resistance of 17 MΩ·cm@25° C. or higher, eg, 18.24 MΩ·cm@25° C., can be supplied from the ion exchange resin device 45 to the second electrode of the cell stack 41 . On the outlet of the second flow path of the second electrode in the cell stack 41, it is connected to return the oxygen (O ₂ ) and the remaining ultrapure water generated by the water decomposition in the cell stack 41 to the water tank 22. The second piping 25. The second pipe 25 is connected to a position higher than the liquid level in the water tank 22 set by the liquid level sensor 29 . Accordingly, when the operation of the tank bank 41 is stopped, the water in the second piping 25 is prevented from flowing back into the tank bank 41 .

However, if the stop time of the tank stack 41 becomes longer, the water remaining in the second piping 25 evaporates and the MEA dries up. If it dries, the diaphragm shrinks and becomes swollen when water is supplied again, and mechanical load is applied to the diaphragm by repeating the dry-wet cycle, and the flow path may be clogged due to rupture or deformation of the diaphragm, or the cell stack 41 may be damaged. Concerns about reduced durability. From such a viewpoint, it is preferable to connect the second pipe 25 to a position lower than the liquid level in the water tank 22 set by the liquid level sensor 29 . However, this alone cannot suppress the backflow of the water in the second piping 25 into the tank stack 41 . In this regard, it is preferable to adopt the configurations of the fifth or sixth embodiment shown below, or other embodiments other than them.

(fifth embodiment)

An electrochemical reaction device 20 according to a fifth embodiment will be described with reference to FIG. 11 . Differences between the electrochemical reaction device 20 shown in FIG. 11 and the electrochemical reaction device 20 of the fourth embodiment shown in FIG. 10 will be mainly described. The electrochemical reaction device 20 shown in FIG. 11 includes a water tank 47 of an overflow structure separated into two tanks of a low water level tank part L and a high water level tank part H by an overflow wall 46 . In the water tank 47 having the overflow wall 46, among the two tanks separated by the overflow wall 46, the one on the water inlet side is the high water level tank part H, and the other on the water outlet side is the low water level tank. Department L. The water supply pipe 48 of the RO membrane device 42 is connected to the low water level tank part L. The pure water (process raw liquid) produced in the RO membrane device 42 is supplied to the low water level tank part L. As shown in FIG. The first pipe 24 which is the water supply pipe to the tank stack 41 is connected to the low water level tank part L. As shown in FIG. The high water level tank part H is connected to the second pipe 25 which is the drain pipe from the tank stack 41 . The ultrapure water (liquid to be treated) treated in the tank stack 41 is returned to the high water level tank part H. Moreover, the 2nd piping 25 is connected to the water below the liquid surface set by the overflow wall 46 of the high water level tank part H. As shown in FIG. Accordingly, the watertightness of the second pipe 25 is maintained.

In the water tank 47 having a double tank structure, the water sent into the high water level tank part H exceeds the overflow wall 46 and is sent into the low water level tank part L. Therefore, the water sent into the high water level tank part H does not mix with the water remaining in the low water level tank part L. FIG. As mentioned above, since the second pipe 25 is connected under the liquid surface of the high water level tank part H, the water returned from the tank stack 41 (ultrapure water having a specific resistance of 17 MΩ·cm or more) will not be kept at the low water level. Water (pure water having a specific resistance in the range of 0.1 to 5 MΩ·cm) in the groove portion L is mixed. Therefore, when the operation of the tank bank 41 is stopped, even if the ultrapure water remaining in the high water level tank part H and the ultrapure water in the second piping 25 flow back into the tank bank 41, the tank bank 41 will not be damaged. performance degradation. That is, the pure water produced in the RO membrane device 42 contains fine particles such as anion components, cation components, and SiO ₂ , although there are few. When they enter the separator, the ionic conductivity is reduced, or they are adsorbed on the catalysts on the first electrode and the second electrode, so that the reaction area of electrochemical reactions such as electrolysis is reduced. However, the ultrapure water only flows backward into the tank stack 41 . That is, the liquid to be treated (ultrapure water) containing pure water as the original treatment liquid does not flow back into the tank stack 41 . Therefore, the performance of the slot stack 41 is not degraded. Deterioration of the cell stack 41 and the electrolysis device 20 can be suppressed.

(sixth embodiment)

An electrochemical reaction device 20 according to a sixth embodiment will be described with reference to FIG. 12 . Differences between the electrochemical reaction device 20 shown in FIG. 12 and the electrochemical reaction devices 20 of the fourth and fifth embodiments shown in FIGS. 10 and 11 will be mainly described. In the electrochemical reaction device 20 shown in FIG. 12 , the RO membrane device 42 is directly connected to the first pipe 24 which is the water supply pipe to the tank stack 41 . A pump 26 and an ion exchange resin device 45 are provided in the first piping 24 . Therefore, pure water as a treatment stock solution produced by the RO membrane device 42 is directly supplied to the ion exchange resin device 45 for producing ultrapure water as a liquid to be treated through the first pipe 24 . The water tank 22 is connected to the second pipe 25 which is the drain pipe from the tank stack 41 . The pipe 49 on the outlet side of the water tank 22 is connected to the upstream side of the pump 26 of the second pipe 25 . A check valve 50 is provided in the piping 49 .

In the electrochemical reaction device 20 having such a configuration, the pure water produced by the RO membrane device 42 is directly sent to the ion exchange resin device 45 without passing through the water tank 22 . The ultrapure water produced by the ion exchange resin device 45 is sent into the tank stack 41 . The water (ultrapure water) discharged from the tank stack 41 is sent into the water tank 22 , passed through the pipe 49 and the ion exchange resin device 45 , and then sent into the tank stack 41 . At this time, since the pure water produced by the RO membrane device 42 is not sent into the water tank 22 , the water remaining in the water tank 22 is basically only the ultrapure water passing through the tank stack 41 . Therefore, when the operation of the tank stack 41 is stopped, even if the ultrapure water stored in the water tank 22 and the ultrapure water in the second piping 25 flow back into the tank stack 41, since the pure water used as the processing raw solution The ultrapure water of the liquid to be treated does not flow back into the cell stack 41 , so similar to the electrochemical reaction device 20 of the fifth embodiment, the performance of the cell stack 41 is not lowered.

The electrochemical reaction device 20 of the sixth embodiment may have the configuration shown in FIG. 13 . FIG. 13 is a diagram showing a modified example of the electrochemical reaction device 20 shown in FIG. 12 . In the electrochemical reaction device 20 shown in FIG. 13 , the RO membrane device 42 is connected to the first pipe 24 similarly to the electrochemical reaction device 20 shown in FIG. 12 . Not only the RO membrane device 42 is connected to the first pipe 24 but also the pipe 56 from the RO membrane device 42 is connected to the ejector 55 provided on the second pipe 24 connected to the outlet of the water tank 22 . The second piping 24 has a pump 26 , a check valve 54 , and an ejector 55 provided in this order on the upstream side of the ion exchange resin device 45 . The ejector 55 is connected to the ion exchange resin device 45 via the first pipe 24 . In Fig. 12, the pump 26 is arranged on the downstream side of the connecting part of the second piping 24 and the piping 56 from the RO membrane device 42. In contrast, in Fig. 13, the piping 56 from the RO membrane device 42 is connected to the second piping 56. The downstream side of the pump 26 in the piping 24 .

The ejector 55 is a jet pump, and has two inlets of relatively high-pressure water inlet (first inlet) 55a and relatively low-pressure water inlet (second inlet) 55b, and one outlet 55c. A water supply port of the pump 26 for spraying relatively high-pressure water is connected to the first inlet 55a. The water supply port of the RO membrane device 42 for spraying relatively low-pressure water is connected to the second inlet 55b. Inside the ejector 55, water with a relatively high pressure (water sprayed from the pump 26/water of the water tank 22) is sprayed from the nozzle, and water with a relatively low pressure (from the RO membrane device 42 The sprayed water) is sprayed in such a manner that it is entrained, thereby making it easy to supply the relatively low-pressure water sprayed from the RO membrane device 42 to the ion exchange resin device 45 . In addition, the eductor 55 also has the effect of mixing relatively high-pressure water and relatively low-pressure water. In this way, the pressure of the water supply port of the RO membrane device 42 is maintained at a low pressure favorable for RO membrane treatment, and the water (RO water) sprayed from the RO membrane device 42 can be supplied to the high-pressure piping, so that ultra-high pressure can be performed immediately. Pure water treatment. Therefore, stagnation of relatively low-purity RO water in the system can be suppressed to a minimum, and thus contamination of the electrochemical device 1 can be effectively suppressed.

(seventh embodiment)

An electrochemical reaction device 20 according to a seventh embodiment will be described with reference to FIGS. 13 and 14 . Differences between the electrochemical reaction device 20 shown in FIGS. 13 and 14 and the electrochemical reaction devices 20 of the fourth and fifth embodiments shown in FIGS. 10 and 11 will be mainly described. In the electrochemical reaction device 20 shown in Figure 13 and Figure 14, the 2nd water tank (gas-liquid separation tank) with gas-liquid separation function is connected on the outlet of the 1st flow path of the 1st electrode of cell stack 41 51. Hydrogen (H ₂ ) generated by water decomposition and remaining water are sent from the first electrode of the cell stack 41 to the second water tank (gas-liquid separation tank) 51 . The configuration of the water tank (first water tank) 22 is the same as that of the fourth electrochemical reaction device 20 shown in FIG. 10 except that the second pipe 25 is connected under the water surface of the first water tank 22 .

However, when the operation of the tank bank 41 is stopped, the following factors can be considered as the main cause for the water remaining in the water tank 22 and the water in the second pipe 25 to flow back into the tank bank 41 . That is, when the operation of the cell stack 41 is stopped, water flows from the second electrode through the diaphragm into the first electrode. Accordingly, it is considered that the water remaining in the water tank 22 and the water in the second piping 25 flow back into the tank bank 41 when the operation of the tank bank 41 is stopped. In order to prevent the water in the water tank 22 and the second piping 25 from flowing back into the cell stack 41, it is only necessary to suppress the flow of water from the second electrode through the diaphragm into the first electrode when the operation of the cell stack 41 is stopped.

Therefore, in the electrochemical reaction device 20 shown in FIG. 13 , the second water tank 51 is provided such that the liquid level of the second water tank (gas-liquid separation tank) 51 is higher than that of the first water tank 22 . Based on the static positions of the second water tank 51 and the first water tank 22, the internal pressure of the second water tank 51 is higher than the internal pressure of the first water tank 22, so the pressure of the tank stack 41 can be suppressed. The water in the first water tank 22 and the second piping 25 flows back into the tank stack 41 . Since the internal pressure of the second water tank 51 is higher than the internal pressure of the first water tank 22, in the electrochemical reaction device 20 shown in FIG. And control the opening and closing operation of the valve 53 . By adopting such a configuration, even if the internal pressure P _H2 of the second water tank 51 is increased compared with the internal pressure P _O2 of the first water tank 22, the pressure of the first water tank 22 and the second water tank 22 when the operation of the tank bank 41 is stopped can be suppressed. 2 Backflow of water in the piping 25 to the tank stack 41.

Example

Next, examples and evaluation results thereof will be described.

(Example 1)

As shown in FIG. 2, the second flow path 12 that constitutes the water tank 22 and the second electrode 3 in the electrochemical reaction cell (electrolytic cell) 1 is connected by a second piping 25 provided with a check valve 28. The formed electrochemical reaction device (electrolysis device) 20. During the operation of the device, oxygen and ultrapure water generated in the second electrode 3 are sent into the water tank 22 through the second pipe 25 . On the other hand, when the device is stopped, the water in the water tank 22 does not flow back into the second electrode 3 through the check valve 28 . At this time, the height difference of the check valve 28 arranged below the liquid level of the water tank 22 is 30 cm, and the minimum working pressure of the check valve 28 based on formula (3) is preferably set above 3 kPa. Therefore, in Embodiment 1, a ball check valve with a minimum working pressure of 5kPa is used.

In the electrochemical reaction device 20 having such a structure, a specific resistance meter is set on the part between the check valve 28 of the second piping 25 and the second flow path 13, and it is confirmed that the water quality does not change from 18.24 MΩ· when the device stops. cm drops considerably. Using such an apparatus, the process of operating at 50A for 1 hour and then stopping for 24 hours was regarded as one time and repeated 300 times. At the initial stage of operation of the device, the voltage was 1.85 V, and the current density was 2 A/cm ² . On the other hand, after repeating 300 times, it was confirmed that the values of the voltage of 1.87 V and the current density of 2 A/cm ² were maintained.

(Example 2)

As shown in FIG. 6, a U-shaped pipe 31 is provided as a second pipe between the water tank 22 and the second flow path 13 in the electrochemical reaction tank (electrolytic tank) 1 so as to form a protrusion upward. 25 on. During the operation of the device, oxygen and ultrapure water generated in the second electrode 3 are sent into the water tank 22 through the second pipe 25 . On the other hand, when the apparatus is stopped, the pump 26 is also stopped immediately after the electrolysis is stopped, so that a generated gas is formed inside the U-shaped piping 31 and the gas remains. As a result, the water in the water tank 22 will not flow back into the second electrode 3 because the gas in the water tank 22 will merge and cut off the liquid flow.

In the electrochemical reaction device 20 having such a structure, by installing a specific resistance meter on the second electrode 3 side rather than the gas storage in the U-shaped piping 31, the portion where the water in the second piping 25 is stored, the When the device was stopped, it was confirmed that the water quality did not drop significantly from 18.24 MΩ·cm. Using such an apparatus, the process of operating at 50A for 1 hour and then stopping for 24 hours was regarded as one time and repeated 300 times. At the initial stage of operation of the device, the voltage was 1.85 V, and the current density was 2 A/cm ² . On the other hand, after repeating 300 times, it was confirmed that the values of the voltage of 1.87 V and the current density of 2 A/cm ² were maintained.

(Example 3)

As shown in FIGS. 6 and 8 , a U-shaped pipe 31 is provided between the water tank 22 and the second flow path 13 in the electrochemical reaction tank (electrolytic tank) 1 so as to protrude upward. on the second piping 25 . Moreover, the gas supply part 32 is connected to the upper part of the U-shaped piping 31, and the structure which can supply gas to the U-shaped piping 31 from the outside is formed. During the operation of the device, oxygen and ultrapure water generated in the second electrode 3 are sent into the water tank 22 through the second pipe 25 . On the other hand, when the apparatus is stopped, the pump 26 is temporarily operated immediately after the electrolysis is stopped, and then gas is injected into the U-shaped pipe 31 from the outside to form a gas pool. As a result, the water in the water tank 22 does not flow back into the second electrode 3 because the gas in the water tank 22 merges and cuts off the liquid flow.

In the electrochemical reaction device 20 having such a structure, by installing a specific resistance meter on the second electrode 3 side rather than the gas storage in the U-shaped piping 31, the portion where the water in the second piping 25 is stored, the When the device was stopped, it was confirmed that the water quality did not drop significantly from 18.24 MΩ·cm. Using such an apparatus, the process of operating at 50A for 1 hour and then stopping for 24 hours was regarded as one time, and was repeated 300 times. At the initial stage of operation of the device, the voltage was 1.85 V, and the current density was 2 A/cm ² . On the other hand, after repeating 300 times, it was confirmed that the values of the voltage of 1.87 V and the current density of 2 A/cm ² were maintained.

(Example 4)

As shown in FIG. 9 , a long pipe 33 is provided on the second pipe 25 between the water tank 22 and the second flow path 13 in the electrochemical reaction cell (electrolytic cell) 1 . Assuming that the impurity concentration of the water in the water tank 22 is 2 ppm, the required piping length when the piping diameter is 1 inch in diameter is calculated from Fick's law. In Example 4, the piping length of the second piping 25 including the long piping 33 was set to 2 m as a sufficient length for which the specific resistance did not drop completely in 24 hours.

In the electrochemical reaction device 20 having such a configuration, a specific resistance meter is installed near the second flow path 13 of the second piping 25, specifically, at a position 5 cm away from the second flow path 13, and it is confirmed that after the device is stopped, The water quality was 15MΩ·cm at 3 hours, 10MΩ·cm at 12 hours, and 7MΩ·cm at 24 hours, and the water quality in the water tank 24 did not drop to 0.1MΩ·cm. Using such an apparatus, the process of operating at 50A for 1 hour and then stopping for 24 hours was regarded as one time, and was repeated 300 times. At the initial stage of operation of the device, the voltage was 1.85 V, and the current density was 2 A/cm ² . On the other hand, after repeating 300 times, it was confirmed that the values of the voltage of 1.89 V and the current density of 2 A/cm ² were maintained.

(comparative example 1)

In FIG. 2 , FIG. 6 , and FIG. 9 , the electrochemical reaction device 20 is formed by connecting the water tank 22 to the second flow path 13 at the shortest distance with a second piping 25 without a backflow suppression mechanism. In the electrochemical reaction device 20 having such a configuration, when the device is stopped, a specific resistance meter is provided between the water tank 22 and the second flow path 13 to measure the specific resistance of water after the device stops. As a result, it was confirmed that the specific resistance of water decreased to about 1 MΩ·cm in about 3 hours, and decreased to 0.1 MΩ·cm in 12 hours. This shows that the water in the water tank 22 flows back into the MEA9. Using such an apparatus, the operation was repeated 300 times under the same conditions as in Example 1. At the initial stage of operation of the device, the voltage was 1.85 V, and the current density was 2 A/cm ² . In contrast, after 300 repetitions, the voltage was raised to 2.25V, and the current density was 2A/cm ² . From the above results, it was confirmed that the deterioration of the electrolytic cell 1 proceeded due to the reverse flow of the water tank 22 when the apparatus was stopped.

It should be noted that the configurations of the above-described embodiments can be applied in combination, respectively, and can also be partially replaced. Here, some embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in other various forms, and various omissions, substitutions, changes, and the like can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

Claims (20)

1. An electrochemical reaction device, comprising:

an electrochemical reaction cell comprising a 1 st electrode having a 1 st flow path, a 2 nd electrode having a 2 nd flow path, and a separator sandwiched between the 1 st electrode and the 2 nd electrode;

a liquid tank that accommodates a liquid to be treated in the 2 nd flow path for supplying the liquid to the 2 nd electrode;

a 1 st pipe that connects an inlet of the 2 nd flow path and the tank and supplies the liquid to be treated to the 2 nd flow path;

a second piping that connects an outlet of the second flow path to the liquid tank and returns the liquid to be treated to the liquid tank; and

and a reverse flow suppressing means provided in the 2 nd pipe for preventing reverse flow of the liquid to be treated flowing in the 2 nd pipe or reducing a reverse flow rate.

2. The electrochemical reaction apparatus according to claim 1, wherein,

the liquid tank is provided with a liquid level sensor,

the 2 nd pipe is connected to a position lower than the liquid level in the liquid tank set by the liquid level sensor.

3. The electrochemical reaction apparatus according to claim 1, wherein the reverse flow suppressing mechanism is provided with a check valve.

4. The electrochemical reaction apparatus of claim 3, wherein the check valve has a swing check valve, a lift check valve, a butt check valve, or a ball check valve.

5. The electrochemical reaction apparatus according to claim 1, wherein the backflow suppressing mechanism comprises a backflow suppressing pipe having a shape capable of forming a gas storage section.

6. The electrochemical reaction apparatus according to claim 5, wherein the backflow suppressing mechanism includes a gas supply portion for supplying a gas to the gas storage portion of the backflow suppressing piping.

7. The electrochemical reaction apparatus according to claim 1, wherein,

the liquid tank is provided with a liquid level sensor,

the 2 nd pipe is connected to a position higher than the liquid level in the liquid tank set by the liquid level sensor.

8. The electrochemical reaction apparatus according to claim 1, wherein,

further comprises a gas-liquid separation tank connected to the outlet of the 1 st flow path,

the gas-liquid separation tank is disposed such that the liquid level in the tank is higher than the liquid level in the tank set by a liquid level sensor provided in the tank.

9. The electrochemical reaction apparatus according to claim 1, further comprising:

a gas-liquid separation tank connected to the outlet of the 1 st flow path, and

a valve provided in a gas discharge pipe of the gas-liquid separation tank;

The valve is controlled so that the internal pressure of the gas-liquid separation tank is higher than the internal pressure of the liquid tank.

10. The electrochemical reaction apparatus according to claim 1, further comprising:

a pure water producing part connected to the liquid tank and supplying pure water to the liquid tank, and

an ultrapure water producing section provided in the 1 st pipe and supplying ultrapure water to the 2 nd flow path of the 2 nd electrode;

the electrochemical reaction tank is configured to electrolyze the ultrapure water.

11. An electrochemical reaction device, comprising:

an electrochemical reaction cell comprising a 1 st electrode having a 1 st flow path, a 2 nd electrode having a 2 nd flow path, and a separator sandwiched between the 1 st electrode and the 2 nd electrode,

a target liquid supply system including a pure water producing section for producing pure water, and an ultrapure water producing section for producing ultrapure water by treating pure water supplied from the pure water producing section, the ultrapure water being supplied as a target liquid to the electrochemical reaction tank, and

a liquid tank for storing the liquid to be treated which is supplied to the electrochemical reaction tank and is treated;

the liquid to be treated supply system is provided with a pure water backflow suppressing means for suppressing backflow of the liquid to be treated containing the pure water from the liquid tank into the electrochemical reaction tank.

12. The electrochemical reaction apparatus according to claim 11, wherein,

the liquid tank is provided with an overflow structure which is separated into a low water level groove part and a high water level groove part through an overflow wall,

a pipe for supplying the deionized water from the deionized water producing portion to the ultrapure water producing portion is connected to the low water level tank portion of the liquid tank, and the deionized water is supplied to the ultrapure water producing portion via the low water level tank portion of the liquid tank,

and a pipe for returning the liquid to be treated from the electrochemical reaction tank to the liquid tank is connected to the high water level tank portion of the liquid tank.

13. The electrochemical reaction apparatus according to claim 11, wherein,

a supply pipe for supplying the pure water from the pure water producing section to the ultrapure water producing section is directly connected to the ultrapure water producing section,

a pipe for returning the liquid to be treated from the electrochemical reaction tank to the liquid tank is connected to the liquid tank, and a pipe for supplying the liquid to be treated from the liquid tank to the electrochemical reaction tank is connected to an upstream side of the ultrapure water production section of the supply pipe via a check valve.

14. The electrochemical reaction apparatus according to claim 11, wherein,

A pipe for supplying the liquid to be treated from the liquid tank to the electrochemical reaction tank is connected to the ultrapure water production section via a pump and an ejector,

a water supply port for supplying the pure water from the pure water producing section is connected to the ejector.

15. An electrochemical reaction method comprising the steps of:

a step of preparing a liquid to be treated by treating the raw liquid to be treated;

a step of supplying the liquid to be treated to a 2 nd flow path of an electrochemical reaction tank, and causing an electrochemical reaction in the electrochemical reaction tank, wherein the electrochemical reaction tank includes a 1 st electrode having a 1 st flow path, a 2 nd electrode having a 2 nd flow path, and a separator sandwiched between the 1 st electrode and the 2 nd electrode; and

and a step of suppressing backflow of the liquid to be treated containing the raw liquid to the 2 nd flow path while stopping the electrochemical reaction of the liquid to be treated.

16. The electrochemical reaction process of claim 15, wherein,

the stock solution is temporarily stored in a tank, and then treated to prepare the solution to be treated,

the liquid to be treated in the electrochemical reaction tank is returned to the liquid tank through a pipe provided with a check valve.

17. The electrochemical reaction process of claim 15, wherein,

the stock solution is temporarily stored in a tank, and then treated to prepare the solution to be treated,

the liquid to be treated in the electrochemical reaction tank is returned to the liquid tank through a backflow suppressing pipe having a shape capable of forming a gas storage portion.

18. The electrochemical reaction process of claim 15, wherein,

the stock solution is treated to prepare the solution to be treated after being temporarily stored in the low water level tank portion of a liquid tank having an overflow structure separated into two tanks, a low water level tank portion and a high water level tank portion by an overflow wall,

the liquid to be treated in the electrochemical reaction tank is returned to the high water level tank portion of the liquid tank.

19. The electrochemical reaction process of claim 15, wherein,

the stock solution is temporarily stored in a tank, and then treated to prepare the solution to be treated,

the liquid to be treated by the electrochemical reaction tank is returned to the liquid tank,

the electrochemical reaction tank includes a gas-liquid separation tank connected to the outlet of the 1 st flow path, and is controlled so that the internal pressure of the gas-liquid separation tank is higher than the internal pressure of the liquid tank.

20. The electrochemical reaction process of claim 15, wherein,

the treatment stock solution is pure water produced by a pure water producing section,

the pure water is directly sent to an ultrapure water production section to produce ultrapure water as the liquid to be treated,

the ultrapure water is sent to the electrochemical reaction tank via a pipe for treatment,

the ultrapure water treated by the electrochemical reaction tank is sent to a liquid tank,

the ultrapure water stored in the liquid tank is sent to a position upstream of the ultrapure water production section of the piping via a check valve.