Electrochemical reaction apparatus and electrochemical reaction method

Abstract

The present application provides an electrochemical reaction device and an electrochemical reaction method. The electrochemical reaction device of an embodiment includes: an electrochemical reaction cell including a first electrode having a first flow path, a second electrode having a second flow path, and a separator sandwiched by the first electrode and the second electrode; a liquid tank for accommodating a treatment liquid supplied to the second flow path of the second electrode; a first pipe connecting an inlet of the second flow path and the liquid tank; a second pipe connecting an outlet of the second flow path and the liquid tank; and a backflow suppression mechanism provided in the second pipe for preventing or reducing a backflow of the treatment liquid flowing in the second pipe.

Description

[0001] This application is based on Japanese Patent Application 2022-011964 (filed on 01 / 28 / 2022) and Japanese Patent Application 2022-118767 (filed on 07 / 26 / 2022), and enjoys priority from the aforementioned applications. This application incorporates the entire contents of the aforementioned applications by reference. Technical Field

[0002] The embodiments of the present invention relate to an electrochemical reaction apparatus and an electrochemical reaction method. Background Technology

[0003] As a representative example of an electrochemical reaction device such as an electrolysis unit, a water electrolysis device is known to produce hydrogen (H2) and oxygen (O2) by electrolyzing water (H2O). This water electrolysis device, for example, includes an electrolytic cell with an anode, a cathode, and a diaphragm such as a polymer electrolyte membrane (PEM) sandwiched between the anode and cathode. In this water electrolysis device, hydrogen (H2) is produced at the cathode and oxygen (O2) at the anode by electrolyzing water (H2O). Water electrolysis cells using such a PEM as a diaphragm (PEM-type water electrolysis cells) are characterized by low operating temperature and high hydrogen purity. However, PEM-type water electrolysis cells, which have diaphragms, suffer from a problem where their performance tends to degrade during start-up and shutdown operations. This problem is not limited to water electrolysis cells; it also exists in diaphragm-equipped electrolysis cells and electrolysis devices (electrochemical reaction units). Summary of the Invention

[0004] The problem to be solved by the present invention is to provide an electrochemical reaction device and an electrochemical reaction method that can suppress performance degradation during start-up and stop operations.

[0005] The electrochemical reaction apparatus of the embodiment includes: an electrochemical reaction tank comprising a first electrode having a first flow path, a second electrode having a second flow path, and a diaphragm sandwiched between the first electrode and the second electrode; a liquid tank for containing a liquid to be treated supplied to the second electrode in the second flow path; a first piping connecting the inlet of the second flow path and the liquid tank, and supplying the liquid to be treated into the second flow path; a second piping connecting the outlet of the second flow path and the liquid tank, and returning the liquid to be treated to the liquid tank; and a backflow suppression mechanism provided on the second piping for preventing backflow of the liquid to be treated flowing in the second piping or reducing the backflow velocity. Attached Figure Description

[0006] Figure 1This is a diagram showing the structure of the electrochemical reaction tank in the electrochemical reaction apparatus of the embodiment and the connection structure between the electrochemical reaction tank and the power source.

[0007] Figure 2 This is a diagram showing the electrochemical reaction apparatus of the first embodiment.

[0008] Figure 3 This is a diagram showing an enlarged portion of the electrochemical reaction apparatus of the first embodiment.

[0009] Figure 4 The graph shows a comparison between the resistivity of water when the electrochemical reaction apparatus of the first embodiment is stopped and the resistivity of water when the electrochemical reaction apparatus without a check valve is stopped.

[0010] Figure 5 The graph shows a comparison of the voltage change over time of the electrochemical reaction apparatus of the first embodiment with the voltage change over time of an electrochemical reaction apparatus without a check valve.

[0011] Figure 6 This is a diagram showing the electrochemical reaction apparatus of the second embodiment.

[0012] Figure 7 This is a diagram showing a portion of the first example of the electrochemical reaction apparatus according to the second embodiment.

[0013] Figure 8 This is a diagram showing a portion of a second example of the electrochemical reaction apparatus according to the second embodiment.

[0014] Figure 9 This is a diagram showing the electrochemical reaction apparatus of the third embodiment.

[0015] Figure 10 This is a diagram showing the electrochemical reaction apparatus of the fourth embodiment.

[0016] Figure 11 This is a diagram showing the electrochemical reaction apparatus of the fifth embodiment.

[0017] Figure 12 This is a diagram showing the electrochemical reaction apparatus of the sixth embodiment.

[0018] Figure 13 It means Figure 12 A diagram showing a modified example of the electrochemical reaction apparatus.

[0019] Figure 14 This is a diagram showing an example of the electrochemical reaction apparatus of the seventh embodiment.

[0020] Figure 15 This is a diagram showing another example of the electrochemical reaction apparatus of the seventh embodiment.

[0021] (Symbol Explanation)

[0022] 1: Electrochemical reaction cell (electrolyzer), 2: First electrode, 3: Second electrode, 4: Diaphragm, 12: First flow path, 13: Second flow path, 20: Electrochemical reaction device (electrolysis device), 22: Water tank, 23: Pure water production device, 24: First piping, 25: Second piping, 26: Pump, 27: Ultrapure water production device, 28: Check valve, 29: Liquid level sensor, 31: U-shaped piping, 32: Gas supply unit, 33: Long piping, 41: Electrochemical reaction cell stack, 46: Overflow wall, 47: Water tank with overflow structure, 51: Gas-liquid separator (second water tank), 53: Valve. Detailed Implementation

[0023] The electrochemical reaction apparatus of the embodiments will now be described with reference to the accompanying drawings. In the embodiments shown below, the same symbols are used to mark the same components, and sometimes descriptions are omitted. The accompanying drawings are schematic diagrams, and the relationship between thickness and planar dimensions, the ratio of thickness of each part, etc., may sometimes differ from reality. The symbols “~” in the following description indicate the range between the upper and lower limits, respectively. In this case, each range includes both the upper and lower limits.

[0024] Reference Figure 1 The structure of the electrochemical reaction cell and the connection structure between the electrochemical reaction cell and the power source of the embodiment of the electrochemical reaction apparatus will be described. Figure 1 The electrochemical reactor 1 shown includes a first electrode 2, a second electrode 3, and a diaphragm 4 sandwiched between the first electrode 2 and the second electrode 3. The diaphragm 4 may be, for example, a solid polymer electrolyte membrane (PEM). When the electrochemical reactor 1 is used as a water electrolyzer, the first electrode 2 is the cathode (reduction electrode / hydrogen electrode), and the second electrode 3 is the anode (oxidation electrode / oxygen electrode). The following description primarily focuses on the case where the electrochemical reactor 1 is used as a water electrolyzer, but is not limited to this. A proton-conducting membrane may be used as the solid polymer electrolyte membrane 4.

[0025] As a constituent material of the proton-conducting PEM, fluoropolymers with sulfonic acid groups can be used, for example. Specific examples of such materials include Nafion (registered trademark), a fluoropolymer formed by the sulfonation polymerization of tetrafluoroethylene by DuPont; Aciplex (registered trademark), manufactured by Asahi Kasei Corporation; and Flommion (registered trademark), manufactured by AGC Corporation. The separator 4 is not limited to solid polymer electrolyte membranes; it can also be a hydrocarbon membrane containing electrolyte components, a membrane containing inorganic substances such as tungstic acid and phosphotungstic acid, or other electrolyte membranes.

[0026] The anode, or second electrode 3, electrolyzes water (H₂O) through an oxidation reaction to generate hydrogen ions (H₂O). + ) and oxygen (O2). The cathode, i.e., the first electrode 2, reacts with hydrogen ions (H+) generated in the anode. + Hydrogen (H2) is generated by reduction. The cathode, i.e., the first electrode 2, has a first catalyst layer 5 and a first charge-donating layer 6. The first catalyst layer 5 is arranged in contact with the membrane 4. The anode, i.e., the second electrode 3, has a second catalyst layer 7 and a second charge-donating layer 8. The second catalyst layer 7 is arranged in contact with the membrane 4. By sandwiching the membrane 4, such as PEM, with the first electrode 2 and the second electrode 3, a membrane electrode assembly (MEA) 9 is formed.

[0027] The first catalyst layer 5, serving as the cathode (i.e., the first electrode 2), can be made of metals such as platinum (Pt), silver (Ag), and palladium (Pd), or alloys containing at least one of Pt, Ag, and Pd (Pt alloys, Ag alloys, Pd alloys). More preferably, Pt and Pt alloys such as PtCo, PtFe, PtNi, PtPd, PtIr, PtRu, and PtSn can be used in the first catalyst layer 5. The second catalyst layer 7, serving as the anode (i.e., the second electrode 3), can be made of, for example, iridium (Ir) oxide, ruthenium (Ru) oxide, palladium (Pd) oxide, Ir composite oxide, Ru composite oxide, and Pd composite oxide. 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, and Pd. Ir oxides and Ir composite oxides are more preferably used as the second catalyst layer 7.

[0028] The first charging layer 6 of the first electrode 2 and the second charging layer 8 of the second electrode 3 can be made of materials with gas diffusion and conductivity. Specifically, porous conductive components are suitable for the first charging layer 6 and the second charging layer 8. The first charging layer 6 and the second charging layer 8 can be made of porous metal components such as Ti, Ta, SUS, Ni, and Pt, metal felt, metal nonwoven fabric wound with metal fibers, carbon paper, carbon cloth, etc. Ti, which has excellent corrosion resistance, is preferably used for the first charging layer 6 and the second charging layer 8, thereby improving durability. Furthermore, by plating these materials with gold or platinum, durability can be further improved.

[0029] MEA9 is sandwiched between cathode diaphragm 10 and anode diaphragm 11, thereby forming electrochemical reaction tank 1. A first flow path 12 is provided on cathode diaphragm 10 for the flow of reactants and products. A second flow path 13 is provided on anode diaphragm 11 for the flow of reactants and products. Sealing components 14 are disposed on the sides of the first catalyst layer 5 and the first charge-donating layer 6, and on the sides of the second catalyst layer 7 and the second charge-donating layer 8, to prevent leakage of gas or liquid from MEA9 and electrochemical reaction tank 1.

[0030] The electrochemical reaction tank 1 is not limited to a single-tank structure; it can also be a stacked tank structure formed by layering multiple electrochemical reaction tanks 1. The structure of the stacked tank is not particularly limited and can be appropriately selected based on the desired voltage and reaction rate. When using multiple electrochemical reaction tanks 1, it is not limited to a stacked tank structure; it can also be a structure formed by arranging multiple electrochemical reaction tanks 1 in a planar manner. Furthermore, planarly arranged tanks can be further stacked. The number of individual tanks included in the electrochemical reaction tank 1 is not particularly limited and can be appropriately selected.

[0031] As the reactant supplied to the electrochemical reaction tank 1, an aqueous solution containing at least one of water, hydrogen, modified gas, methanol, ethanol, formic acid, etc., can be used. When the electrochemical reaction tank 1 in the embodiment is a water electrolyzer, pure water (e.g., pure water with a resistivity of 0.01 MΩ·cm or more and 5 MΩ·cm or less) is preferred, and ultrapure water (e.g., ultrapure water with a resistivity of 17 MΩ·cm or more) is even more preferred. The electrochemical reaction tank 1 in the embodiment is not limited to an electrolyzer for water electrolysis. It can be used in various electrolyzers, such as a carbon dioxide electrolyzer, which also uses oxides as catalysts. In addition, the electrochemical reaction tank 1 is not limited to an electrolyzer and can also be a fuel cell tank, etc.

[0032] The first electrode 2 and the second electrode 3 of the electrochemical reaction tank 1 are electrically connected to the voltage application mechanism (power supply) 15. A voltage measuring unit 16 and a current measuring unit 17 are provided in the circuit connecting the power supply 15 and the first electrode 2 and the second electrode 3. The power supply 15 is controlled to operate by a control unit 18. The control unit 18 controls the power supply 15 to apply voltage to the electrochemical reaction tank 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 tank 1. The measurement information is sent to the control unit 18. The current measuring unit 17 is inserted into the voltage application circuit for the electrochemical reaction tank 1 and measures the current flowing in the electrochemical reaction tank 1. The measurement information is sent to the control unit 18.

[0033] The control unit 18, for example, is composed of a computer such as a PC or a microcomputer, which processes the data signals output from each part and outputs necessary control signals to each component. The control unit 18 also has a storage device, which controls the output of the power supply 15 according to the program stored in the storage device and based on the measured information, performing control such as applying voltage or changing the load on the electrochemical reaction tank 1. When the electrochemical reaction tank 1 is used for a battery reaction, a voltage is applied to the electrochemical reaction tank 1. When the electrochemical reaction tank 1 is used for a reaction other than a battery reaction, such as a hydrogen generation reaction based on water electrolysis and a carbon dioxide electrolysis reaction, a voltage is applied to the electrochemical reaction tank 1. The electrochemical reaction apparatus of the embodiment is configured, for example, to perform an electrochemical reaction by applying a voltage between the first electrode 2 and the second electrode 3.

[0034] (First Embodiment)

[0035] Next, refer to Figure 2 For those with Figure 1 The electrochemical reaction apparatus 20 of the first embodiment of the electrochemical reaction tank 1 shown will be described here. Here, the configuration of the electrochemical reaction apparatus 20 when applied to a water electrolysis apparatus for electrolyzing water will be mainly described, but the electrochemical reaction apparatus of the embodiment is not limited to this, and may also be a carbon dioxide electrolysis apparatus, etc. Figure 2 The electrochemical reaction apparatus (electrolysis apparatus) 20 shown includes a water supply system (processed liquid supply system) 21, which supplies water as the processed liquid to the second electrode 3 of the electrochemical reaction cell (electrolysis cell) 1.

[0036] The water supply system 21 includes a water tank 22 for containing the liquid to be treated, which is supplied to the second flow path 13 of the second electrode 3. A pure water production device 23 is connected to the water tank 22, from which pure water, serving as the treatment stock solution, can be supplied. The pure water production device 23 can be, for example, a reverse osmosis (RO) membrane device. Tap water W or similar water can be supplied to the pure water production device 23 as raw water. The resistivity of tap water W is approximately 0.01 MΩ·cm at 25°C or less. If such water W is treated using a pure water production device 23 such as an RO membrane device, pure water (treatment stock solution) with a resistivity of approximately 0.01 to 5 MΩ·cm at 25°C can be produced. This pure water can then be supplied to the water tank 22.

[0037] 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 tank 1, and is connected to the inlet IN of the water tank 22 and the second flow path 13. A pump 26 and an ultrapure water production device 27 are provided in the supply pipe, i.e., the first pipe 24. The ultrapure water production device 27 may be, for example, an ultrapure water device using ion exchange resin. Pure water contained in the water tank 22 is pumped into the ultrapure water production device 27 via the pump 26. If pure water with a resistivity in the range of 0.01 to 5 MΩ·cm@25°C is treated with an ultrapure water production device 27 such as an ion exchange resin device, ultrapure water with a resistivity of 17 MΩ·cm@25°C or higher, such as 18.24 MΩ·cm@25°C, can be produced as the treated liquid. 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. During the flow in the second flow path 13, water electrolysis is performed by the second electrode 3, which serves as the anode.

[0038] A second piping 25 is connected to the outlet OUT of the second flow path 13 of the second electrode 3 for returning the oxygen (O2) generated by water decomposition and the remaining water to the water tank 22. The second piping 25 (also called the oxygen piping) is a return piping that returns the oxygen (O2) generated by water decomposition and the remaining water to the water tank 22, connecting the outlet OUT of the second flow path 13 to the water tank 22. The water tank 22 has a gas-liquid separation function, and the separated oxygen (O2) can be recovered from the water tank 22 as needed. The water contained in the water tank 22 circulates via the first piping 24, pump 26, ultrapure water production device 27, second flow path 13, and second piping 25. A check valve 28 is provided on the second piping 25 as a backflow suppression mechanism, as detailed later.

[0039] In water electrolysis based on the second electrode 3, oxygen (O2) and hydrogen ions (protons / H+) are generated. + Protons (H+) are transported from the second electrode 3 to the first electrode 2 of the electrochemical reaction tank 1 through the diaphragm 4. + Since water is also supplied from the second electrode 3 to the first electrode 2 through the diaphragm 4, a water tank with gas-liquid separation function can be connected to the outlet of the first flow path 12 of the first electrode 2 as needed. Protons (H) supplied to the first electrode 2 + ) and electrons (e) reaching the first electrode 2 through the external circuit - The reaction produces hydrogen (H2). The hydrogen (H2) produced in the first electrode 2 is recovered by being discharged directly from the first electrode 2 or via a water tank to the outside.

[0040] Next, regarding Figure 2The operation of the electrochemical reaction apparatus 20 shown will be explained. When water electrolysis is carried out, if a voltage is applied to the second electrode 3, which serves as the anode, from an external power source, water (H2O) is electrolyzed, and the reaction shown in equation (1) occurs.

[0041] 2H₂O→O₂+4H + +4e - (1)

[0042] The protons (H) produced at this time + The electrons are transported through the diaphragm 4 to the first electrode 2, which serves as the cathode. Furthermore, electrons (e...) - The hydrogen is produced in the first electrode 2 via an external circuit. The first electrode 2, which serves as the cathode, produces hydrogen through the reaction shown in equation (2).

[0043] 4H + +4e - →2H2 (2)

[0044] Hydrogen and oxygen can be produced through the reactions of the above formulas (1) and (2).

[0045] 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 piping 25. In this configuration, when a backflow suppression mechanism such as a check valve 28 is not installed in the second piping 25, there are concerns that when the operation of the electrolysis unit 20 is stopped, the pure water supplied from the pure water production unit 23 in the water tank 22 may flow back into the second electrode 3 via the second piping 25 and the second flow path 13, or that impurities may diffuse according to the concentration gradient. If pure water flows into the second electrode 3, since the second electrode 3 is porous, pure water with a resistivity in the range of 0.1 to 5 MΩ·cm contained in the water tank 22 may also reach the diaphragm 4 and the first electrode 2. Small amounts of anionic and cationic components, particles such as SiO2 contained in such pure water may enter the interior of the diaphragm 4, thereby causing adverse effects such as a decrease in ionic conductivity or an extreme reduction in the reaction area of ​​electrochemical reactions such as electrolysis due to adsorption on the catalyst on the first electrode 2 and the second electrode 3. The backflow of pure water from such water tank 22 into electrochemical reaction tank 1 is the main reason for the reduced performance of electrochemical reaction tank 1.

[0046] Therefore, in the electrochemical reaction apparatus (electrolysis apparatus) 20 of the first embodiment, a check valve 28 is provided as a backflow suppression mechanism 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. When the operation of the electrolysis apparatus 20 is stopped, the check valve 28 can prevent the pure water from the water tank 22 from flowing back to the second electrode 3 via the second piping 25 and the second flow path 13. By suppressing the backflow of pure water from the water tank 22 to the second electrode 3, the electrochemical reaction apparatus (electrolysis apparatus) 20 can be stopped with the second flow path 13 and the second electrode 3 filled with ultrapure water. Therefore, the performance of the electrochemical reaction tank 1 when the electrochemical reaction apparatus (electrolysis apparatus) 20 is stopped can be maintained.

[0047] As a check valve 28 for suppressing the backflow of pure water from the water tank 22 into the second electrode 3, the minimum backflow differential pressure P (kPa) is preferably a value or higher as expressed by the following formula (3).

[0048] Δh×ρ×g(3)

[0049] Δh is the liquid level in water tank 22 minus the height of check valve 28, ρ is the liquid density, and g is the acceleration due to gravity. By using a check valve 28 with a minimum backflow differential pressure P equal to or greater than the value expressed by equation (3), it is possible to effectively prevent the backflow of pure water in water tank 22 into the second electrode 3 when the operation of the electrolysis unit 20 is stopped. Examples of check valves 28 with such a configuration include swing check valves, lift check valves such as Smolensky type (also known as slow-closing type) check valves, wafer check valves, and ball check valves. On the other hand, valves with multiple teardrop-shaped rings (so-called Tesla valves) that allow the liquid flowing inside the pipe to meander are not suitable.

[0050] In the electrochemical reaction apparatus (electrolysis device) 20 of the first embodiment, the second piping 25, which is equipped with a check valve 28, is preferably connected below the liquid surface of the water tank 22, i.e., in the water. The pure water production apparatus 23, for example, is based on... Figure 3 As shown, water W is supplied to water tank 22 as the raw water for the treated water (electrolyzed water). Water tank 22 has a liquid level sensor 29 installed inside it. The liquid level sensor can also be a laser-type liquid level gauge or the like installed outside water tank 22. When the liquid level in water tank 22 is lower than the lower limit value set by liquid level sensor 29, water supply pump 30, which supplies water W from pure water production unit 23 to water tank 22, is activated to supply water into water tank 22. Therefore, it is preferable to connect the second piping 25 to a position lower than the liquid level in water tank 22 set by liquid level sensor 29.

[0051] By connecting the second pipe 25 to a position lower than the liquid level set by the liquid level sensor 29, a liquid seal can be maintained through the second pipe 25 while the backflow of pure water in the water tank 22 is suppressed by the check valve 28. Even when the second pipe 25 is connected to a position higher than the liquid level, backflow of water in the second pipe 25 can be suppressed. However, if the stop time is long, the MEA9 will dry out due to the evaporation of water remaining in the second pipe 25. If it dries out, the diaphragm 4 will shrink and may become swollen when water is supplied again. Repeating this wet-dry cycle will put a mechanical load on the diaphragm 4, resulting in flow path blockage caused by rupture or deformation of the diaphragm 4. Furthermore, this is not preferable from the viewpoint of the durability of the electrolyzer 1.

[0052] Figure 4 The resistivity of water when the electrochemical reaction device (electrolysis device) 20 is stopped (when the current stops) is shown by comparing it with the resistivity of water when the electrolysis device without a check valve is stopped. Figure 5 The voltage change over time of the electrochemical reaction device (electrolysis device) 20 is shown by comparing it with the voltage change over time of an electrolysis device without a check valve. For example... Figure 4 As shown, by installing a check valve 28 in the second piping 25, the decrease in resistivity caused by the backflow of water from the water tank 22 to the second electrode 3 can be suppressed. Additionally, as... Figure 5 As shown, by installing a check valve 28 in the second piping 25, the performance degradation of the electrolyzer 1 caused by the backflow of water in the water tank 22 can be suppressed.

[0053] (Second Implementation)

[0054] Reference Figures 6-8 The electrochemical reaction apparatus 20 of the second embodiment will be described. Figure 6 In the electrochemical reaction apparatus 20 shown, a U-shaped pipe 31, configured in a reverse U-shape (convex upward orientation), serves as a backflow suppression mechanism in the second piping 25 at the outlet OUT of the second flow path 13 connecting the water tank 22 and the second electrode 3. Other components are similar to... Figure 2 The electrochemical reaction apparatus 20 shown in the first embodiment is the same. Based on the U-shaped piping 31 arranged in a reverse U-shape, when the water flowing in the second piping 25 is stopped, as... Figure 7 As shown, oxygen (O2) mixed in the water undergoes gas-liquid separation within the U-shaped pipe 31, forming a gas retention section G by remaining in the upper part of the U-shaped pipe 31. By forming this gas retention section G within 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, liquid merging between the water tank 22 and the second electrode 3 is prevented, and backflow of pure water PW from the water tank 22 into the second electrode 3 is prevented.

[0055] The U-shaped pipe 31, serving as a backflow suppression mechanism, is an example of a backflow suppression pipe. The backflow suppression pipe is not limited to a U-shaped pipe, as long as it has a shape that allows for the formation of a gas retention section G through gas-liquid separation. Preferably, the backflow suppression pipe has a shape that facilitates the formation of a gas retention section G inside the pipe and prevents natural leakage of gas from the gas retention section G. Examples of such pipes include the U-shaped pipe 31 and V-shaped pipes. When gas in the gas-liquid mixture discharged from the second electrode 3 remains in the U-shaped pipe 31, if the pump 26 is operated shortly after electrolysis stops, all the gas will leak out of the second pipe 25. To retain the generated gas during electrolysis within the U-shaped pipe 31 as a gas retention section G, it is preferable to stop the pump 26 immediately after the gas generation based on electrolysis ceases.

[0056] Alternatively, the gas retention section G can be formed by gas-liquid separation of the gas (e.g., O2) in the gas-liquid mixture discharged from the second electrode 3, as described above. Figure 8 As shown, gas is supplied from the external gas supply unit 32 to the gas storage section G forming the U-shaped pipe 31. The gas supplied from the gas supply unit 32 is not particularly limited; it can be oxygen (O2), a gas generated during electrolysis, or other gases such as nitrogen (N2), argon (Ar), or air. When supplying gas from the external gas supply unit 32, pump 26 can be stopped as long as the liquid level in the gas-liquid mixture of the U-shaped pipe 31 does not drop.

[0057] When using a backflow suppression piping system such as the U-shaped piping 31, it is preferable to connect the second piping 25 at a position lower than the liquid level in the water tank 22. The liquid level in the water tank 22 is set by a liquid level sensor, similar to the first embodiment. This allows for maintaining a liquid-tight seal via the second piping 25 while suppressing backflow of pure water within the water tank 22 through the gas retention area G formed in the backflow suppression piping system such as the U-shaped piping 31. This helps to prevent a decline in the characteristics and durability of the electrolyzer 1.

[0058] (Third Implementation)

[0059] Reference Figure 9 The electrochemical reaction apparatus 20 of the third embodiment will be described. Figure 9In the electrochemical reaction apparatus 20 shown, a long pipe 33 is provided in the second pipe 25, which connects the water tank 22 and the outlet OUT of the second flow path 13 of the second electrode 3, as a backflow suppression pipe. During operation, the generated oxygen and ultrapure water move into the water tank 22 through the second pipe 25 containing the long pipe 33. When the electrochemical reaction apparatus 20 is stopped, pure water flows back from the water tank 22 to the second electrode 3. Correspondingly, by sufficiently extending the length of the second pipe 25 containing the long pipe 33 (for example, by several tens of times relative to the shortest distance of the second pipe 25), the time for pure water to travel from the water tank 22 to the second electrode 3 can be extended.

[0060] The appropriate length of the second piping 25 can be calculated using Fick's law based on the impurity concentration of the water contained in the water tank 22 and the piping diameter. That is, Fick's law can be used to calculate the length of the distance by which impurities in the water diffuse through the second piping 25 to reach the second electrode 3. Therefore, for example, by considering the time the electrochemical reaction device 20 is stopped, the length of the second piping 25, including the long piping 33, can be set such that the resistivity of the water reaching the second electrode 3 is not less than 5 MΩ·cm. In cases where the downtime is long, it is preferable to further extend the piping length. Thus, by sufficiently extending the length of the second piping 25 using the long piping 33, the time for pure water to reach the second electrode 3 from the water tank 22 is extended, thereby maintaining the second flow path 13 and the second electrode 3 filled with ultrapure water for a longer period. Therefore, the deterioration of the electrolyzer 1 and the electrolysis device 20 can be suppressed.

[0061] (Fourth implementation)

[0062] Reference Figure 10 The electrochemical reaction apparatus 20 of the fourth embodiment will be described. Figure 10 In the middle, it is shown that Figure 1 The electrochemical reactor shown is a stack of multiple layers forming an electrochemical reactor pile 41. Its other basic components are similar to... Figure 2 The electrochemical reaction apparatus 20 shown is largely the same. The following mainly focuses on... Figure 2 The electrochemical reaction device 20 shown and Figure 10 The differences in the electrochemical reaction apparatus 20 shown will be explained. Figure 10 The electrochemical reaction device 20 shown is Figure 2Similarly, the electrochemical reaction apparatus 20 shown includes a water tank 22 as a liquid container for holding the liquid to be processed in the second flow path supplied to 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. Upstream of the carbon filter device 43, a solenoid valve 44 is provided, electrically connected to a liquid level sensor 29 installed in the water tank 22. When the liquid level in the water tank 22, as measured by the liquid level sensor 29, is lower than a lower limit, the solenoid valve 44 is opened, supplying pure water to the water tank 22 via the carbon filter device 43 and the RO membrane device 42.

[0063] A pump 26 and an ion exchange resin unit 45, serving as an ultrapure water production apparatus, are installed in the water supply piping to the stack 41, namely the first piping 24. Ultrapure water with a resistivity of, for example, 18.24 MΩ·cm@25°C, and having a specific resistance of 17 MΩ·cm@25°C or higher can be supplied from the ion exchange resin unit 45 to the second electrode of the stack 41. At the outlet of the second flow path of the second electrode in the stack 41, a second piping 25 is connected to return the oxygen (O2) generated by the decomposition of water in the stack 41 and the remaining ultrapure water to the water tank 22. The second piping 25 is connected at a position higher than the liquid level in the water tank 22 set by the liquid level sensor 29. Thus, when the stack 41 is stopped, backflow of water from the second piping 25 into the stack 41 is suppressed.

[0064] However, if the downtime of the tank 41 becomes prolonged, the MEA will dry out due to the evaporation of water remaining in the second piping 25. If it dries out, the diaphragm shrinks and may become swollen when water is supplied again. Repeating this wet-dry cycle places a mechanical load on the diaphragm, raising concerns about flow path blockage due to diaphragm rupture or deformation, or a decrease in the durability of the tank 41. From that perspective, it is preferable to connect the second piping 25 at a position lower than the liquid level in the water tank 22 set by the liquid level sensor 29. However, this alone cannot prevent backflow of water from the second piping 25 into the tank 41. Therefore, it is preferable to adopt the configuration of the fifth or sixth embodiment shown below, or other embodiments besides those shown below.

[0065] (Fifth Embodiment)

[0066] Reference Figure 11 The electrochemical reaction apparatus 20 of the fifth embodiment will be described. Mainly... Figure 11 The electrochemical reaction device 20 shown is Figure 10 The differences of the electrochemical reaction apparatus 20 of the fourth embodiment shown will be explained. Figure 11The electrochemical reaction apparatus 20 shown includes a water tank 47 with an overflow structure that separates the water into a low-level tank L and a high-level tank H via an overflow wall 46. In the water tank 47 with the overflow wall 46, the side separating the two tanks is designated as the high-level tank H (water inlet side) and the side as the low-level tank L (water outlet side). A feed water pipe 48 of the RO membrane unit 42 is connected to the low-level tank L. Pure water (treatment stock solution) produced in the RO membrane unit 42 is supplied to the low-level tank L. A feed water pipe 24 to the tank stack 41, namely the first pipe 24, is connected to the low-level tank L. A drain pipe 25 from the tank stack 41, namely the second pipe 25, is connected to the high-level tank H. The treated ultrapure water (treated liquid) from the tank stack 41 is returned to the high-level tank H. Furthermore, the second pipe 25 is connected to the water below the liquid level set by the overflow wall 46 of the high water level tank section H. This maintains a water seal on the second pipe 25.

[0067] In the water tank 47 with a dual-tank structure, water fed into the high-level tank H exceeds the overflow wall 46 and is fed into the low-level tank L. Therefore, the water fed into the high-level tank H will not mix with the water remaining in the low-level tank L. As described above, since the second pipe 25 is connected below the liquid surface of the high-level tank H, the water returned from the tank stack 41 (ultrapure water with a resistivity of 17 MΩ·cm or higher) will not mix with the water remaining in the low-level tank L (pure water with a resistivity in the range of 0.1 to 5 MΩ·cm). Therefore, even if the ultrapure water remaining in the high-level tank H and the ultrapure water in the second pipe 25 flow back into the tank stack 41 when the operation of the tank stack 41 is stopped, the performance of the tank stack 41 will not degrade. In other words, the pure water produced in the RO membrane device 42 contains, although in small amounts, anionic and cationic components, particles such as SiO2. These substances enter the membrane, reducing ionic conductivity, or adsorb onto the catalysts on the first and second electrodes, thus reducing the reaction area for electrochemical reactions such as electrolysis. However, ultrapure water only flows back into the tank 41. That is, the treated liquid (ultrapure water) containing the pure water used as the treatment stock solution does not flow back into the tank 41. Therefore, the performance of the tank 41 is not degraded. Deterioration of the tank 41 and the electrolysis unit 20 can be suppressed.

[0068] (Sixth Embodiment)

[0069] Reference Figure 12 The electrochemical reaction apparatus 20 of the sixth embodiment will be described. Mainly... Figure 12 The electrochemical reaction device 20 shown is Figure 10 and Figure 11 The differences between the electrochemical reaction apparatus 20 in the fourth and fifth embodiments shown will be explained. Figure 12In the electrochemical reaction apparatus 20 shown, the RO membrane device 42 is directly connected to the water supply pipe to the tank 41, namely the first pipe 24. A pump 26 and an ion exchange resin device 45 are installed in the first pipe 24. Therefore, the pure water produced by the RO membrane device 42 as the treatment stock solution is directly supplied via the first pipe 24 to the ion exchange resin device 45 used to produce ultrapure water as the treated solution. The drain pipe from the tank 41, namely the second pipe 25, is connected to the water tank 22. The outlet pipe 49 of the water tank 22 is connected upstream of the pump 26 in the second pipe 25. A check valve 50 is installed in the pipe 49.

[0070] In the electrochemical reactor 20 with this configuration, pure water produced by the RO membrane device 42 is directly fed into the ion exchange resin device 45 without passing through the water tank 22. Ultrapure water produced by the ion exchange resin device 45 is fed into the reactor 41. Water discharged from the reactor 41 (ultrapure water) is fed into the water tank 22, then through the piping 49 and the ion exchange resin device 45, and finally back into the reactor 41. Since pure water produced by the RO membrane device 42 is not fed into the water tank 22, the water remaining in the water tank 22 is essentially only ultrapure water from the reactor 41. Therefore, even if the ultrapure water remaining in the water tank 22 and the ultrapure water in the second piping 25 flow back into the reactor 41 when the reactor 41 is stopped, the ultrapure water containing pure water as the treatment stock solution does not flow back into the reactor 41. Therefore, similar to the electrochemical reactor 20 of the fifth embodiment, the performance of the reactor 41 is not degraded.

[0071] The electrochemical reaction apparatus 20 of the sixth embodiment may have Figure 13 The structure shown. Figure 13 It means Figure 12 A diagram showing a modified example of the electrochemical reaction apparatus 20. Figure 13 In the electrochemical reaction apparatus 20 shown, with Figure 12 Similarly, in the electrochemical reaction apparatus 20 shown, the RO membrane unit 42 is connected to the first piping 24. In addition to connecting the RO membrane unit 42 to the first piping 24, a piping 56 from the RO membrane unit 42 is also connected to an ejector 55 located on a second piping 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 arranged sequentially upstream of the ion exchange resin unit 45. The ejector 55 is connected to the ion exchange resin unit 45 via the first piping 24. Figure 12 In this configuration, a pump 26 is located downstream of the connection between the second piping 24 and the piping 56 from the RO membrane unit 42. Figure 13 In this process, the piping 56 of the RO membrane unit 42 will be connected to the downstream side of the pump 26 in the second piping 24.

[0072] The ejector 55 is a jet pump with two inlets: a high-pressure water inlet (first inlet) 55a and a low-pressure water inlet (second inlet) 55b, and one outlet 55c. A water inlet for ejecting the high-pressure water is connected to the first inlet 55a. A water inlet for ejecting the low-pressure water is connected to the second inlet 55b. Inside the ejector 55, high-pressure water (water ejected from the pump 26 / water tank 22) is ejected from the nozzle, and under this force, it is ejected in a manner that entrains low-pressure water (water ejected from the RO membrane device 42), thereby facilitating the supply of the low-pressure water ejected from the RO membrane device 42 to the ion exchange resin device 45. Additionally, the ejector 55 also has the effect of mixing high-pressure and low-pressure water. Therefore, the pressure at the inlet of the RO membrane unit 42 is maintained at a low pressure that is favorable for RO membrane treatment, and water (RO water) ejected from the RO membrane unit 42 can be supplied to the high-pressure piping, enabling immediate ultrapure water treatment. Thus, the retention of relatively low-purity RO water within the system can be minimized, thereby effectively suppressing contamination of the electrochemical device 1.

[0073] (Seventh Embodiment)

[0074] Reference Figure 13 and Figure 14 The electrochemical reaction apparatus 20 of the seventh embodiment will be described. Mainly... Figure 13 and Figure 14 The electrochemical reaction device 20 shown is Figure 10 and Figure 11 The differences between the electrochemical reaction apparatus 20 in the fourth and fifth embodiments shown will be explained. Figure 13 and Figure 14 In the electrochemical reaction apparatus 20 shown, a second water tank (gas-liquid separator) 51 with gas-liquid separation function is connected to the outlet of the first flow path of the first electrode of the tank stack 41. Hydrogen (H2) generated by water decomposition and the remaining water are fed into the second water tank (gas-liquid separator) 51 from the first electrode of the tank stack 41. Regarding the configuration of the water tank (first water tank) 22, except that the second piping 25 is connected below the water surface of the first water tank 22, it is connected to... Figure 10 The fourth electrochemical reaction apparatus 20 shown is identical.

[0075] However, when the tank stack 41 is stopped, the main reason for the backflow of water remaining in the water tank 22 and the second pipe 25 into the tank stack 41 can be considered as follows: When the tank stack 41 is stopped, water flows from the second electrode into the first electrode via the diaphragm. Therefore, it is considered that when the tank stack 41 is stopped, water remaining in the water tank 22 and the second pipe 25 will flow back into the tank stack 41. To prevent such backflow of water from the water tank 22 and the second pipe 25 into the tank stack 41, when the tank stack 41 is stopped, it is sufficient to suppress the flow of water from the second electrode into the first electrode via the diaphragm.

[0076] Therefore, in Figure 13 In the electrochemical reaction apparatus 20 shown, the second water tank 51 is positioned such that the liquid level of the second water tank (gas-liquid separator) 51 is higher than that of the first water tank 22. Based on this static position of the second water tank 51 and the first water tank 22, the internal pressure of the second water tank 51 is higher than that of the first water tank 22, thus suppressing the backflow of water from the first water tank 22 and the second piping 25 into the tank 41 when the tank stack 41 is stopped. Because the internal pressure of the second water tank 51 is higher than that of the first water tank 22, therefore... Figure 14 In the electrochemical reaction apparatus 20 shown, a valve 53 is installed in the gas discharge pipe 52 of the second water tank 51, and the opening and closing operation of the valve 53 is controlled. By adopting this configuration, even with a pressure P relative to the internal pressure P of the first water tank 22... O2 Increase the internal pressure P of the second water tank 51 H2 It can also suppress the backflow of water from the first water tank 22 and the second piping 25 into the tank 41 when the tank 41 is stopped from operating.

[0077] Example

[0078] Next, the embodiments and their evaluation results will be described.

[0079] (Example 1)

[0080] like Figure 2 As shown, an electrochemical reaction apparatus (electrolysis apparatus) 20 is constructed by connecting the water tank 22 and the second flow path 12 of the second electrode 3 in the electrochemical reaction tank (electrolyzer) 1 with a second pipe 25 equipped with a check valve 28. When the apparatus is running, oxygen and ultrapure water generated in the second electrode 3 are sent into the water tank 22 via the second pipe 25. On the other hand, when the apparatus is stopped, the water in the water tank 22 will not flow back into the second electrode 3 through the check valve 28. At this time, the height difference of the check valve 28, which is located below the liquid level in the water tank 22, is 30 cm, and it is preferable to set the minimum operating pressure of the check valve 28 based on formula (3) to be 3 kPa or more. Therefore, in Example 1, a ball check valve with a minimum operating pressure of 5 kPa is used.

[0081] In the electrochemical reaction apparatus 20 with this configuration, a resistivity meter is installed on the section between the check valve 28 of the second piping 25 and the second flow path 13 to confirm that the water quality has not significantly decreased from 18.24 MΩ·cm when the apparatus is stopped. Using this apparatus, a process of operating at 50A for 1 hour and then stopping for 24 hours is considered as one cycle, and this cycle is repeated 300 times. At the initial stage of operation, the voltage is 1.85V and the current density is 2A / cm². 2 In contrast, after 300 repetitions, it was confirmed that the voltage remained at 1.87V and the current density at 2A / cm². 2 The value of .

[0082] (Example 2)

[0083] like Figure 6 As shown, a U-shaped pipe 31 is installed on the second pipe 25 between the water tank 22 and the second flow path 13 in the electrochemical reaction tank (electrolyzer) 1, with the U-shaped pipe 31 protruding upwards. During operation, oxygen and ultrapure water generated in the second electrode 3 are fed into the water tank 22 via the second pipe 25. Conversely, when the device is stopped, the pump 26 is also stopped immediately after electrolysis, causing generated gas to form inside the U-shaped pipe 31, resulting in gas retention. Therefore, the water in the water tank 22 is prevented from flowing backwards into the second electrode 3 due to the presence of gas, thus cutting off the liquid flow.

[0084] In the electrochemical reaction apparatus 20 with this configuration, a resistivity meter is installed in the water retention section of the second pipe 25, closer to the second electrode 3 than the gas retention section in the U-shaped pipe 31. This ensures that the water quality does not significantly decrease from 18.24 MΩ·cm when the apparatus is stopped. Using this apparatus, a cycle of operating at 50 A for 1 hour and then stopping for 24 hours is considered one cycle, and this cycle is repeated 300 times. At the initial stage of operation, the voltage is 1.85 V and the current density is 2 A / cm². 2 In contrast, after 300 repetitions, it was confirmed that the voltage remained at 1.87V and the current density at 2A / cm². 2 The value of .

[0085] (Example 3)

[0086] like Figure 6 and Figure 8As shown, a U-shaped pipe 31 is installed on the second pipe 25 between the water tank 22 and the second flow path 13 in the electrochemical reaction tank (electrolyzer) 1, with the U-shaped pipe 31 protruding upwards. Furthermore, a gas supply unit 32 is connected to the upper part of the U-shaped pipe 31, forming a configuration that allows gas to be supplied to the U-shaped pipe 31 from the outside. During operation, oxygen and ultrapure water generated in the second electrode 3 are fed into the water tank 22 via the second pipe 25. On the other hand, when the device is stopped, gas is injected into the U-shaped pipe 31 from the outside by temporarily running the pump 26 immediately after electrolysis stops, thus creating gas retention. As a result, the water in the water tank 22 is prevented from flowing back into the second electrode 3 due to the presence of gas, thus preventing backflow.

[0087] In the electrochemical reaction apparatus 20 with this configuration, a resistivity meter is installed in the water retention section of the second pipe 25, closer to the second electrode 3 than the gas retention section in the U-shaped pipe 31. This ensures that the water quality does not significantly decrease from 18.24 MΩ·cm when the apparatus is stopped. Using this apparatus, a cycle of operating at 50A for 1 hour and then stopping for 24 hours is considered one cycle, and this cycle is repeated 300 times. At the initial stage of operation, the voltage is 1.85V and the current density is 2A / cm². 2 In contrast, after 300 repetitions, it was confirmed that the voltage remained at 1.87V and the current density at 2A / cm². 2 The value of .

[0088] (Example 4)

[0089] like Figure 9 As shown, a long pipe 33 is installed on the second pipe 25 between the water tank 22 and the second flow path 13 in the electrochemical reaction tank (electrolyzer) 1. Assuming the impurity concentration of the water in the water tank 22 is 2 ppm, the necessary pipe length for setting the pipe diameter to 1 inch is calculated using Fick's law. In Example 4, as a sufficient length to prevent the resistivity from completely decreasing over 24 hours, the pipe length of the second pipe 25, including the long pipe 33, is set to 2 m.

[0090] In the electrochemical reaction apparatus 20 with this configuration, a resistivity meter is installed near the second flow path 13 of the second piping 25, specifically 5 cm away from the second flow path 13. It is confirmed that the water quality is 15 MΩ·cm after 3 hours, 10 MΩ·cm after 12 hours, and 7 MΩ·cm after 24 hours, and the water quality in the water tank 24 does not drop to 0.1 MΩ·cm. Using this apparatus, a cycle of operating at 50A for 1 hour and then stopping for 24 hours is considered as one cycle, and this cycle is repeated 300 times. At the initial stage of operation, the voltage is 1.85V and the current density is 2A / cm². 2In contrast, after 300 repetitions, it was confirmed that the voltage remained at 1.89V and the current density at 2A / cm². 2 The value of .

[0091] (Comparative Example 1)

[0092] exist Figure 2 , Figure 6 ,and Figure 9 In this electrochemical reaction apparatus 20, the water tank 22 is connected to the second flow path 13 via a second pipe 25 without a backflow suppression mechanism, using the shortest distance. In this configuration, the resistivity of the water after the apparatus is stopped is measured by placing a resistivity meter between the water tank 22 and the second flow path 13. The results show that the resistivity of the water drops to approximately 1 MΩ·cm in about 3 hours and to 0.1 MΩ·cm in 12 hours. This indicates that the water in the water tank 22 is flowing back into the MEA9. Using this apparatus, the operation was repeated 300 times under the same conditions as in Example 1. During the initial operation of the apparatus, the voltage was 1.85 V and the current density was 2 A / cm². 2 In contrast, after 300 repetitions, the voltage rose to 2.25V, and the current density was 2A / cm². 2 The above results confirm that the deterioration of electrolytic cell 1 was caused by the backflow of water tank 22 when the device was stopped.

[0093] Furthermore, the configurations of the above-described embodiments can be combined and applied separately, and partial substitutions can also be made. Several embodiments of the present invention have been described here, but these embodiments are merely examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other ways, and various omissions, substitutions, modifications, etc., can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, and are also included within the scope of the invention described in the claims and its equivalents.

Claims

1. An electrochemical reaction apparatus, comprising: An electrochemical reaction cell includes a first electrode having a first flow path, a second electrode having a second flow path, and a diaphragm sandwiched between the first electrode and the second electrode; A liquid tank containing the liquid to be processed for supplying to the second electrode in the second flow path; The first piping connects the inlet of the second flow path to the liquid tank and supplies the liquid to be processed into the second flow path; The second piping connects the outlet of the second flow path to the liquid tank and returns the treated liquid to the liquid tank; and A backflow suppression mechanism is provided on the second pipe to prevent backflow of the liquid being treated flowing in the second pipe or to reduce the backflow velocity. Further features include: A pure water production unit connected to the liquid tank and supplying pure water to the liquid tank, and An ultrapure water manufacturing unit is provided on the first piping and supplies ultrapure water to the second flow path of the second electrode; The electrochemical reaction tank is constructed by electrolyzing the ultrapure water. The backflow suppression mechanism includes a check valve or a backflow suppression piping with a shape that can form a gas retention area.

2. The electrochemical reaction apparatus according to claim 1, wherein, The liquid tank is equipped with a liquid level sensor. The second piping is connected at a position lower than the liquid level in the tank as set by the liquid level sensor.

3. The electrochemical reaction apparatus according to claim 1, wherein, The check valve can be a swing check valve, a lift check valve, a wafer check valve, or a ball check valve.

4. The electrochemical reaction apparatus according to claim 1, wherein, The backflow suppression mechanism includes a gas supply section for supplying gas to the gas retention section of the backflow suppression piping.

5. The electrochemical reaction apparatus according to claim 1, wherein, The liquid tank is equipped with a liquid level sensor. The second piping is connected at a position higher than the liquid level in the tank as set by the liquid level sensor.

6. The electrochemical reaction apparatus according to claim 1, wherein, It further includes a gas-liquid separator connected to the outlet of the first flow path. The gas-liquid separator is configured such that the liquid level inside is higher than the liquid level inside the separator as set by a liquid level sensor installed on the separator.

7. The electrochemical reaction apparatus according to claim 1, wherein, Further features include: A gas-liquid separator connected to the outlet of the first flow path, and A valve installed on the gas discharge pipe of the gas-liquid separator; The valve is controlled in such a way that the internal pressure of the gas-liquid separator is higher than the internal pressure of the liquid tank.

8. An electrochemical reaction apparatus, comprising: An electrochemical reaction vessel includes a first electrode having a first flow path, a second electrode having a second flow path, and a diaphragm sandwiched between the first electrode and the second electrode. The treated liquid supply system includes a pure water production unit for producing pure water and an ultrapure water production unit for producing ultrapure water by treating the pure water supplied from the pure water production unit, and supplies the ultrapure water to the electrochemical reactor as the treated liquid. A liquid tank containing the treated liquid that has been supplied to the electrochemical reactor for processing; The treated liquid supply system includes a pure water backflow suppression mechanism, which suppresses the backflow of the treated liquid containing pure water from the liquid tank into the electrochemical reaction tank. The pure water backflow suppression mechanism is equipped with a check valve or a backflow suppression piping with a shape that can form a gas retention area.

9. The electrochemical reaction apparatus according to claim 8, wherein, The pure water backflow suppression mechanism is achieved through the following mechanism: The liquid tank has an overflow structure that separates it into a low-water-level tank and a high-water-level tank via an overflow wall. The piping supplying the pure water from the pure water production unit to the ultrapure water production unit is connected to the low-level tank of the liquid tank, and the pure water is supplied to the ultrapure water production unit via the low-level tank of the liquid tank. The piping that returns the treated liquid from the electrochemical reaction tank to the liquid tank is connected to the high water level tank section of the liquid tank.

10. The electrochemical reaction apparatus according to claim 8, wherein, The pure water backflow suppression mechanism is implemented through the following mechanism: the supply pipeline for supplying pure water from the pure water manufacturing unit to the ultrapure water manufacturing unit is directly connected to the ultrapure water manufacturing unit. The piping that returns the liquid to be treated from the electrochemical reaction tank to the liquid tank is connected to the liquid tank, and the piping that supplies the liquid to be treated from the liquid tank to the electrochemical reaction tank is connected upstream of the ultrapure water production unit via the check valve.

11. The electrochemical reaction apparatus according to claim 8, wherein, The pure water backflow suppression mechanism is achieved through the following mechanism: The piping supplying the liquid to be treated from the tank to the electrochemical reaction vessel is connected to the ultrapure water production unit via a pump and an injector. The water outlet from which the pure water is sprayed from the pure water production unit is connected to the injector.

12. An electrochemical reaction method comprising the following steps: The process of preparing the liquid to be treated by processing the raw solution; A process of supplying the liquid to be treated into a second flow path of an electrochemical reaction tank, causing the liquid to undergo an electrochemical reaction in the electrochemical reaction tank, wherein the electrochemical reaction tank includes a first electrode having a first flow path, a second electrode having a second flow path, and a diaphragm sandwiched between the first electrode and the second electrode; and The process of stopping the electrochemical reaction of the treated liquid while suppressing the backflow of the treated liquid containing the treatment stock solution into the second flow path.

13. The electrochemical reaction method according to claim 12, wherein, The treatment stock solution is temporarily contained in a liquid tank and then processed in order to prepare the solution to be treated. The treated liquid, after being processed by the electrochemical reactor, is returned to the liquid tank via a piping equipped with a check valve.

14. The electrochemical reaction method according to claim 12, wherein, The treatment stock solution is temporarily contained in a liquid tank and then processed in order to prepare the solution to be treated. The treated liquid, after being processed by the electrochemical reaction tank, is returned to the liquid tank via a backflow suppression pipe having a shape that can form a gas retention section.

15. The electrochemical reaction method according to claim 12, wherein, The treatment stock solution is temporarily contained in the low-level tank of the liquid tank, and then processed to prepare the treatment solution. The liquid tank has an overflow structure that separates the low-level tank and the high-level tank by an overflow wall. The treated liquid, after being processed by the electrochemical reaction tank, is returned to the high-water-level tank section of the liquid tank.

16. The electrochemical reaction method according to claim 12, wherein, The treatment stock solution is temporarily contained in a liquid tank and then processed in order to prepare the solution to be treated. The treated liquid, after being processed by the electrochemical reaction tank, is returned to the liquid tank. The electrochemical reaction tank includes a gas-liquid separator connected to the outlet of the first flow path, and is controlled such that the internal pressure of the gas-liquid separator is higher than the internal pressure of the liquid tank.

17. The electrochemical reaction method according to claim 12, wherein, The treatment stock solution is pure water manufactured by the pure water manufacturing department. The pure water is directly sent to the ultrapure water manufacturing unit to produce ultrapure water as the treated liquid. The ultrapure water is piped to the electrochemical reaction tank for treatment. The ultrapure water treated by the electrochemical reaction tank is then sent to a liquid tank. The ultrapure water contained in the liquid tank is sent to the upstream side of the ultrapure water production unit of the piping via a check valve.

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